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->''"They were independent, separate stories. But now...the stories are combining, that's why the worlds are becoming one."''
-->-- '''[[Series/KamenRiderKiva Wataru Kurenai]]''', ''Series/KamenRiderDecade''

When an author or creator takes two previously unrelated works and puts them into a single, shared {{continuity}}.

No, it's not about welding two weapons together to make a double barrel cannon. That would be ''cannon'' welding, and that would be [[MoreDakka awesome]].

[[SpeculativeFiction Sci-fi]] and fantasy authors don't always write all their novels in the same {{continuity}}. A budding new author's first published book might be about {{space pirate}}s in the 27th century, while his sophomore effort might instead be about 21st century scientists reverse-engineering a flying saucer. In response to popular demand, he might end up writing a {{sequel}} to one, or even both of these novels. Flash forward about 20 years -- the author has grown wealthy from writing stories about Captain Flash Orangebeard and Dr. Smith of Mars, but he's running out of ideas and the two [[LongRunner long-running series]] are in danger of getting stale. What does he do to keep the public's interest, and breathe new life into the storylines?

''Combine them!''

Many long-lived genre authors tend to resort to Canon Welding, usually at a later point in their career. They combine two or more distinct series they've created into a single {{continuity}}. This isn't just a one-off {{Crossover}}; for series with radically different premises, the foundations of one or both stories can be altered forever.

By combining the two series together, the author can introduce fans of one series to characters they may not be familiar with, inducing them to go out and buy the works in that series, and hopefully attract high sales from fans of both storylines. When done well, it can add a more epic feel to the tale, explore aspects of the two storylines not previously delved into, and make lots of money for the author and his publisher (and there are many examples of this, perhaps most famously ''Film/LordOfTheRings''). When done poorly, especially with stories with radically different settings or styles, it looks and feels like a shallow money-grab and can potentially be a [[JumpTheShark shark-jumping]] moment for both series.

ModularFranchise is when it's done at a corporate level. Compare SharedUniverse, which can be created through Canon Welding if it wasn't shared from the beginning.
----
!!Examples:

[[foldercontrol]]

[[folder:Cross-Media]]
* The Chris Boucher ''Franchise/DoctorWhoExpandedUniverse'' Literature/PastDoctorAdventures novel ''Corpse Marker'' and semi-licenced audio series called ''Kaldor City'' places ''Series/BlakesSeven'' in the Franchise/{{Whoniverse}}. Specifically, these show that ''Blake's 7'' takes place in the same time period as Boucher's popular ''Series/DoctorWho'' story "[[Recap/DoctorWhoS14E5TheRobotsOfDeath The Robots of Death]]".
** This was very nearly canon, as it happens; the [[OutsideContextVillain invasion force from another galaxy]] from the finale of Season 2 of ''Blake's 7'' were intended to be the Daleks at one point, but for one reason or another the idea was dropped.
** Creator/DouglasAdams' character Professor Chronotis from the novel ''Literature/DirkGentlysHolisticDetectiveAgency'' originally came from Adams' TV script ''Shada'' (which was only partly filmed due to an electricians' strike). In the Dirk Gently novel, it's not spelled out that Chronotis is a Time Lord in hiding, for copyright reasons, but it's clearly meant to be the same character. There's even an oblique little reference at the end that a [[TheNthDoctor strange young man]] came and permanently disabled his time machine, while the POV character wasn't around...
* ''VideoGame/SuperRobotWars'' is already a {{Crossover}} series, with nearly as many {{canon}}s as it has games - most entries take place in their own [[{{Continuity}} continuities]], created by fusing together the stories of whichever mecha shows are featured in that particular game. But there are a few characters who show up in multiple [[{{Continuity}} continuities]], and while most of them are AlternateUniverse versions of each other, Gilliam Yeager, whose gimmick involves hopping between universes, has been implied to be the same person in all his appearances, no matter what {{continuity}} you're in. Which in turn means that any games with Gilliam in them would be part of the same {{multiverse}}.
** And then there's the ''VideoGame/EndlessFrontier'' series, which [[{{Crossover}} crosses over]] with both ''[[VideoGame/SuperRobotWarsOriginalGeneration Original Generation]]'' (which features Gilliam) and the even-more-mega-{{Crossover}} ''VideoGame/NamcoXCapcom''. And since ''VideoGame/NamcoXCapcom'' contains everything from ''Franchise/StreetFighter'' to ''VideoGame/{{Xenosaga}}'' (Which also crosses over to ''Endless Frontier'') to ''VideoGame/{{Klonoa}}'', there are versions of all of those characters (not the same versions that exist in their original games, but still, ''a'' version) in the ''SRW'' {{multiverse}}. With ''VideoGame/ProjectXZone'' any Capcom and Namco series not already included into the ''SRW'' multiverse will most likely be added however there will also be dozens of Creator/{{Sega}} series in the game like ''VideoGame/VirtuaFighter'' and ''VideoGame/ValkyriaChronicles''.
* The ''Franchise/KamenRider'' franchise has had this going since the beginning. The Showa-era shows ([[Series/KamenRider original]] through ''Series/KamenRiderBlackRX'') explicitly took place in the same universe, and the previous Riders would often show up near the end of the latest series to help out [[TheHero the current hero]]. The movies produced in the hiatus years (''Film/ShinKamenRiderPrologue'', ''Film/KamenRiderZO'', ''Film/KamenRiderJ'') and the Heisei shows (''[[Series/KamenRiderKuuga Kuuga]]'' onwards) abandoned this, except for a few rare {{Crossover}} events. ''Series/KamenRiderDecade'' deliberately says that the Heisei shows all occupy their own separate universe...and then has the first nine (''Kuuga'' to ''[[Series/KamenRiderKiva Kiva]]'') forcibly merged, with Decade forced to travel to alternate versions of said worlds in an attempt to fix everything...and then there's the ''Decade'' movie ''All Riders vs. Great Shocker'', which [[{{Crossover}} crosses over]] with the entire Showa-era universe as well. ''Movie War 2010'' also adds ''Series/KamenRiderDouble'' to the mix. Then ''Series/KamenRiderFourze'' decided to just bite the bullet and imply at the end of episode 2 that every show in the franchise is set in the same universe, with WordOfGod saying that they're going to {{Retcon}} the elements of ''Decade'' that didn't work. For extra humor, ''Series/KamenRiderKabuto'' has a brief in-character cameo by the actor who plays Rider-1 in TheRemake ''Film/KamenRiderTHEFIRST'', and ''Series/KamenRiderRyuki'' had a DVD-exclusive joke episode where the protagonist [[AllJustADream dreams]] that he teams up with Series/KamenRiderAgito to battle Agito's EvilTwin.
** ZO and J fight a multi-seasonal batch of monsters in Kamen Rider World (8-minute theme park thingy, may not be {{canon}} but never said not to be, and not contradicting anything) which puts ''all three'' hiatus movies (yes, Shin provided a monster) into old-school KR {{continuity}}. Kuuga's mention of a Professor Hongo (and an imitation of him, which means he ''must'' have known ''the'' Hongo) put Kuuga and Agito into it as well. However, Decade makes the {{multiverse}} more complicated with its {{alternate universe}}s bearing variable resemblence to - and ''rarely'' literally being - the worlds of the actual series it's [[{{Crossover}} crossing over]] with. We even get Black and Black RX as separate worlds, as well as Kuuga and Agito, with alternate versions of some of the same people. Even moreso, late in ''Double'' a member of [[NebulousEvilOrganisation Foundation X]] can be seen looking over data on OOO's Core Medals. Nothing came of this for over a year, until the crossover ''Film/KamenRiderXKamenRiderFourzeAndOOOMovieWarMegamax'' revealed that Foundation X would be playing a role, this time using the Astro Switches from ''Fourze''...and that Double and the first seven Showa Riders would be teaming up with Fourze and OOO. Given how Astro Switches pretty much ''are'' Gaia Memories this makes some sense (except for the Last One thing).
** Some worlds have versions of Riders of other worlds with no dimension-hopping. For example, Dark Kabuto, Dark Kiva, Ryuga, and Orga live in a world where monsters rule, and have no connection to ''Kabuto, Kiva, Ryuki,'' or ''Faiz.'' It's the ''second'' Ryuga we meet, and no, the first wasn't in the World of Ryuki, either.) It also means Double and OOO take place in the World of the Rider War, as Double does no dimension hopping to meet Decade, and OOO does no dimension hopping to meet Double. (That last point, though, is pretty much complicated by [[NonSerialMovie the sheer canon inconsistencies]] between ''Series/KamenRiderOOO'' and ''Movie Wars Core''.)
** As closest anyone can figure, here's how the Kamen Rider multiverse seems to work: The Showa era Riders and the 3 intermediate Riders (Shin, ZO, and J) take place in a singular continuity as we saw them. The Heisei era shows from Kuuga to Kiva (plus most of their movies) each take place in their own continuity with the notable exception of Kiva and Den-O, and the possible exception of Kuuga and Agito. Decade takes place all over the multiverse, but the opening episode and and the end of Movie Wars takes place in the same continuity as Double (who's appearance in Decade's movie can be chalked up to his universe meshing with Decade's). Speaking of Double, all of the series from Double onwards exist in the same continuity, which also contains variations of every Rider from Ichigo to Kiva, just not exactly as we saw them in the series. As far as OOO is concerned, his movies seem to be more canon than his actual series is.
** Decade's own MindScrew-itiude and AWizardDidIt attitude makes it nigh useless for working out continuity issues [[PowerCreepPowerSeep or finally answering which of your favorite Riders can kick the other's ass]]. Post-Decade teamup occasions not requiring any dimension-hopping (as it was with pre-Decade teamup occasions) would seem to have all things ''Kamen Rider'' in one universe, with past Riders still out there after they leave our sight (like any character in any show who has been PutOnABus.) It would seem that none of the AR Worlds were the one universe KR usually takes place in.
** However, don't put away your migraine medicine ''just yet: OOO, Den-O, All Riders: Let's Go, Kamen Rider'' would have the ''Decade'' World of Kuuga BigBad instead of the ''Series/KamenRiderKuuga'' Big Bad representing the Grongi in the LegionOfDoom, which would have welded Decade and its madness right back in...if it weren't for the fact that the movie's ending implicitly makes the whole ordeal non-canon to everything by virtue of [[spoiler:settling on a CloseEnoughTimeline where, in regards to ''Kamen Rider OOO'', Hina doesn't know Eiji]]. (Also, ''every'' character who appeared in Decade had their updated design from that series instead of their original designs, but that can be ignored - ''you'd'' use the shiny Decade suits instead of making all new ones that ''don't look as good'' in order to perfectly match the 1970s versions.)
** More out-of-series welding: ''Let's Go, Kamen Rider'' also gives us cameos of Inazuman, {{Kikaider}}, Kikaider 01, and even ''Series/KaiketsuZubat.'' So basically everything with ShotaroIshinomori's name on it officially coexists now, even if you didn't take ''Goranger vs. JAKQ'' (which had ''Series/KamenRiderV3, Series/KamenRiderAmazon'', and ''{{Kikaider}}'' stated to be fighting the same LegionOfDoom overseas.) seriously before. Then one of the ''Kamen Rider Fourze'' movies goes and introduces Inazuman... based on ''Inazuman'' the manga, not the show, and so not the Inazuman encountered in ''Let's Go Kamen Riders.''
** ''MaskedRider'', the not well received American adaptation of ''Black RX'' was launched with a PoorlyDisguisedPilot in a ''Series/MightyMorphinPowerRangers'' episode; much later, ''Series/PowerRangersInSpace'' [[{{Crossover}} crossed over]] with ''Series/NinjaTurtlesTheNextMutation'', which makes all three American series share a Verse. All three are produced by Saban, which wasn't so bad back then, but as of 2009...
** Take all the {{crossover}}s above, put two plus two with the ''Kamen Rider'' and ''TMNT'' {{multiverse}}s separately established by ''Decade'' and ''TurtlesForever'' respectively[[note]]Incidentally, both are 2009 anniversary specials.[[/note]], and toss in both the {{Canon}}ical ''Series/SamuraiSentaiShinkenger'' arc of ''Decade'' and ''TeenageMutantNinjaTurtlesSmashUp'' for kicks. End result? ''Kamen Rider'', ''Power Rangers'', ''Franchise/SuperSentai'', ''TMNT'', the ''Franchise/UltraSeries'', and ''VideoGame/RavingRabbids'' are all part of the multiverse. It's gotten to the point that, near as anyone can tell of the yet-unreleased ''Film/KamenRiderXSuperSentaiSuperheroTaisen'' movie, nobody except Marvelous and Decade know what the hell is going on. Even the narrator is baffled. And with Compati Hero Series ''The Great Battle IV'' this would tie in ''Franchise/{{Gundam}}'', the ''Ultra Series'', and ''Kamen Rider'', et al. with the aforementioned ''VideoGame/SuperRobotWars'' and...well. Just let your imagination go wild, one supposes.
* Speaking of ''Franchise/{{Transformers}}'', it was split from its very beginning into separate comic and cartoon [[{{Continuity}} continuities]]. However, this rapidly splintered further and further, with different comics in different [[{{Continuity}} continuities]] being introduced, anime series being created, the introduction of the ''WesternAnimation/BeastWars'' and ''WesternAnimation/BeastMachines'' ranges which combine elements from previous [[{{Continuity}} continuities]], [[Film/{{Transformers}} the live-action movies]] and so on.
** In the mid-2000s, writer Simon Furman ruled that every single ''{{Transformers}}'' {{continuity}} forms part of a massive {{multiverse}} of different timelines, dimensions and universes, and sometimes featured {{Crossover}}s in his stories (for example, the 'Generation One' Galvatron and several others making a cameo appearance in a ''TransformersArmada'' comic). He also ruled that Unicron and Primus are constant forces in this {{multiverse}}, and though they can be destroyed in one reality their consciousness lives on in another. Curiously, his [[ComicBook/TheTransformersIDW next range of comics for IDW]] seemed to separate from this idea altogether.
** The [[{{Canon}} canonical]] explanation of how Multiversal Singularities work, using [[Film/{{Transformers}} The Fallen]] as an example, [[MindScrew truly has to be read]] [[VoodooShark to be believed.]] [[http://tfwiki.net/wiki/Multiversal_singularity Link.]]
** It gets better. Courtesy of Axiom Nexus, '''any''' Transformers series can interact with any other.
** Even better, the Transformers franchise itself was an amalgamation of several unrelated lines of Japanese die-cast toys (Jetfire/Skyfire was a [[{{Macross}} VF-1 Valkyrie]]), with most of the welding done by the fine folks at Marvel Comics.
** The Transformers also went full circle when they crossed over with [[Comicbook/TheAvengers the New Avengers]]. To say nothing of their participation in the ''Infestation'' crossovers at IDW, which suggests that, among others, StarTrek and the TeenageMutantNinjaTurtles are also part of the same multiverse.
** ''Regeneration One'', the continuation of the original Marvel series (disregarding the ''Generation 2'' series), concludes that the Grand Plan of Primus is to eventually create one "optimal" universe that comprises the best features of the various realities of the multiverse. And yes, Simon Furman wrote that series. (It also features a team-up of [[spoiler: Rodimus Prime and his cross-dimensional counterparts]].)
* ShotaroIshinomori's later ''SkullMan'' manga incorporates his earliest concept for the titular character of ''Kamen Rider'', monsters from said show, Series/KamenRider himself, appearances of Joe Shimamura from the anime ''{{Cyborg 009}}'', as well as cameos from ''Series/HimitsuSentaiGoranger'', ''RobotDetective'', ''{{Inazuman}}'', and ''{{Kikaider}}.'' A later anime version of ''SkullMan'' has a DownerEnding that connects it even more explicitly to ''{{Cyborg 009}}'': [[spoiler:Skull Man is defeated and turned into Black Ghost, the BigBad of ''009''.]]
* The OVA ''GiantRobo: The Day The Earth Stood Still'' and its companion manga ''The Day The Earth Burned'' incorporates practically ''all'' of Mitsuteru Yokoyama's work, including the first magical girl ''SallyTheWitch'', the tokusatsu show ''Iga No Kagemaru'', the eponymous giant robots, and historical characters from both the ''Literature/WaterMargin'' and ''Literature/RomanceOfTheThreeKingdoms''.
* Once Matt Tracker figure was released as ''Specialist Tracker'' in one of GIJoe toy series, Series/{{MASK}} has been ''adopted'' into G.I.Joe Universe.
* [[InvertedTrope Inverted]] with the ''StarshipTitanic'' and ''Franchise/TheHitchhikersGuideToTheGalaxy''. Despite both featuring similar Starship Titanics which undergo similar events in similar settings, the game [[FridgeLogic explicitly states that they're different universes.]]
* ''WitchGirlsAdventures'' is a [[TheVerse 'verse]] created almost entirely through Canon Welding. The 'verse [[BleachedUnderpants started as a fetish e-zine called "The Shrinking Sorceress"]] by MANGA GRAPHIX, dedicated to sorceresses transforming people into animals and inanimate objects. Later on, many of the same people went on to write ''Witch Girls Tales'', theoretically a comic about young witches getting into mischief with their powers, and several characters and concepts from MANGA GRAPHIX stories ended up in the new 'verse. Completely independently, a different author wrote a comic called "Princess Lucinda," about the titular princess' love for wickedness and transforming people over the slightest offense. The ''WitchGirlsAdventures'' game was created as a team-up between Channel M (the reconstituted MANGA GRAPHIX) and Abby Soto (the creator of Princess Lucinda), using characters from "The Shrinking Sorceress" (including some that hadn't yet appeared in ''Tales''), ''Witch Girls Tales'', and ''Princess Lucinda'' all in a single standalone universe.
* ''ReturnToLabyrinth'':
** The OEL manga sequel to the film ''Film/{{Labyrinth}}'', has cameos by Uncle Traveling Matt from ''Series/FraggleRock'' and the devils from the "Soldier & Death" episode of ''Series/TheStoryTeller'', establishing that these JimHenson Company works share a [[TheVerse Verse]].
** Fraggle Rock (the location) is basically a canon-welding tool, since it's established in the fourth season of the show that the Rock can magically link to many locations - some in our world, some in others. Uncle Matt also turned up in ''TheMuppetsTakeManhattan'', and other creatures from the Rock have appeared as extras in Muppet productions throughout the 1990s. In turn, the Muppets share a universe with ''SesameStreet''. Additionally, one creature occasionally seen in Fraggle Rock resembles Fizzgig from ''TheDarkCrystal'', suggesting another link.
* The guest characters of the ''SoulSeries'' imply that the series shares a multiverse with ''Franchise/TheLegendOfZelda'', ''Franchise/StarWars'', ''VideoGame/GodOfWar'', ''KeroroGunso'', ''ImageComics'' (or at least ''{{Spawn}}''), ''VideoGame/TalesOfSymphonia'' and ''Franchise/AssassinsCreed''.
** The Soul Series is also seem to take place in the distant past of the ''VideoGame/{{Tekken}}'' universe due the presence of [[LegacyCharacter Yoshimitsu]] in every installment of both series.
* Video game ''BlairWitchproject I: Rustin Parr'' sets the original Blair Witch movie and video game ''VideoGame/{{Nocturne}}'', made by the same creators in one world.
** And apparently the first ''VideoGame/BloodRayne'' game implies several times that it's set in the same world as ''Nocturne''.
* There is a crossover between ''Franchise/WonderWoman'' and ''Literature/FafhrdAndTheGrayMouser''. The latter's world was adapted into ''Tabletopgame/DungeonsAndDragons'' setting. Of course, there was a fair amounts of retcons in Franchise/TheDCU and revised editions of D&D, but it's quite possible that the link estabilishing connection between the three still exist in some form.
** Thanks to the d20 edition of TabletopGame/CallOfCthulhu you can play as Dungeons and Dragons characters in Call of Cthulhu and introduce the Cthulhu Mythos into Dungeons and Dragons. It however doesn't stop there as the Call of Cthulhu sourcebook known as The ''Malleus Monstrorum'' not only mentions every major [[CthulhuMythos Mythos]] entity, the book also manages to throw in ''Film/TheThing1982'', The Martians of ''Literature/TheWarOfTheWorlds'', and ''TheWickerMan'' and several of Creator/StephenKing's characters as avatars of Nyarlathotep;
* Creator/NeilGaiman's ''Literature/AmericanGods'' had a cameo from Delirium of the Endless from ''ComicBook/TheSandman''. Given Endless' nature it is entirely vague if that means the book takes place in DCUniverse or just is the part of the same multiverse.
[[/folder]]

[[folder:Anime and Manga]]
* Manga creator Creator/GoNagai does this often with his various works, although ''Anime/MazingerZ'' and ''Anime/UFORoboGrendizer'' were already part of one continuity from Grendizer's get-go.
** ''Anime/ShinMazinger'' is quickly reaching a critical level of this, with a woman from ''Violence Jack'' turning out to be [[spoiler: Kouji Kabuto's ''mother''.]]
** ''Manga/ViolenceJack'' has incorporated ''Manga/{{Devilman}}'' and later ''Manga/DevilmanLady'' as taking place in one Universe [[spoiler: that resets itself and all main characters are really incarnations of Akira Fudou]]. And because the series is also DeconstructorFleet for all other Creator/GoNagai's manga, there are many theories incorporating them into it [[spoiler: in all incarnations, which is possible thanks to the nature of this world]]. Cameos and crossovers between his works are so often it's pretty easy. Then there's ''Devilman Grimoire'', where Jun Fudo and Aoi Kurosaki from DevilmanLady are shown to be teachers at Akira and Miki's school. They are also lovers. Alphonse and Himura, from the 1970s Devilman anime series, also feature.
* Gosho Aoyama's three main works ''Manga/DetectiveConan'', ''MagicKaito'', and ''{{Yaiba}}!'', have the tendency to merge into one universe. ''MagicKaito'' was more or less put on hold in favor of ''Manga/DetectiveConan'', but its characters occur so frequently in ''Manga/DetectiveConan'' to be the latter's recurring characters. Although, Aoyama also drew the line: ''Manga/DetectiveConan'' does not deal with the daily life of the ''MagicKaito'' characters.
** On the other hand, ''MagicKaito'' is definitively ''in'' the same universe of ''{{Yaiba}}!''; the characters went to the same school called Ekoda, and the ''Manga/DetectiveConan'' OVA Conan vs Kaitou Kid vs Yaiba was originally a ''MagicKaito'' story arc (and not AllJustADream), in which Kaito attempts to steal a magic sword, just before he found out what he was meant to be going after. Not to say, Aoko's gossip mill friend Keiko's "very reliable source" is Sayaka, the main girl in ''{{Yaiba}}!''.
* The various series in the Franchise/{{Gundam}} franchise often get crammed into one of the (as of right now) eight universes that make up the Gundam multiverse [[ContinuitySnarl no matter how much they contradict one another]]. Among them are [[AlternateUniverse Universal Century, Future Century, After Colony, After War, Correct Century, Cosmic Era, Anno Domini, and Advanced Generation]].
** ''Anime/TurnAGundam'' broadly hinted that each of the different [[AlternateContinuity Alternate Continuities]] ([[WordOfGod yes, including the ones that were made after it, like Cosmic Era, Anno Domini, and Advanced Generation]]) of the ''Franchise/{{Gundam}}'' [[{{Ficton}} franchise]] to date were part of a grander history -- with plenty of [[TheEndOfTheWorldAsWeKnowIt disasters]] to [[AfterTheEnd reset the clock]] between settings.
* The mangaka group Creator/{{CLAMP}} has been known for self-crossovers for many years, but their twin series ''TsubasaReservoirChronicle'' and ''Manga/XxxHOLiC'' are meant to tie all their works--both present-day and fantasy--into a single continuity.
* ''PrettyCureAllStars.'' 14 magical girls from 4 different continuities save the day. Awesome.
** The second All Stars-movie features 17 magical girls from 5 different continuities. From the previews it seems to feature some of the different baddies, too.
*** ''All Stars DX 3'' ups the number to 21 from 6 continuities and the brand-new New Stage brings it to a grand total of 28 from 7. It overlaps with RememberTheNewGuy as a lot of Cures that show up in one movie weren't in the movie before that.
**** ''All Stars New Stage'' delivers a {{Retcon}} of sorts now stating that 23 magical girls from 6 different continuities saved the day. Then 5 more from the 7th hopped in and it was madness.
** Interestingly, it seems that ''SmilePrettyCure'' is attempting a bit of a Canon Weld experiment themselves - an episode midway through reveals that Yayoi's mother works for Fairy Drop, the store owned by [[Anime/HeartcatchPrettyCure Erika Kurumi's]] mother. And said mother is mentioned, at least by last name.
* Eiichiro Oda re-used Ryuuma, a character from his one-shot manga ''Monsters'', as a (zombified) villain in ''Manga/OnePiece'' and his home country was mentioned to be part of the New World (the second half of the Grand Line). He later confirmed that ''Monsters'' was incorporated into the backstory of the setting.
* ''MahouSenseiNegima'' reveals that all of Ken Akamatsu's major works exist in the same universe. The ties between Negima and ''LoveHina'' are obvious with Setsuna being a Shinmeiryuu swordswoman, which is lead by the Aoyama family from ''Love Hina''; the reference to ''Manga/AILoveYou'' is found in a single panel, although it's kinda important, as [[spoiler: the protagonist of that series is implied to have written the code that enables [[RobotGirl Chachamaru]] to have a soul.]]
* Before he gave the world ''Manga/DragonBall'', AkiraToriyama's first popular series was a comedy called ''DoctorSlump'', about a robot girl and the slob scientist who created her causing havoc in a weird place called Penguin Village. About a year into ''Dragon Ball'', Toriyama had Goku visit Penguin Village and meet most of the ''Slump'' cast, thus joining the two series into one universe. This was mostly done as an attempt to use ''Dr. Slump'''s popularity to help increase readership of ''Dragon Ball'', as it wasn't the huge hit it would eventually become yet. In contrast, the crossover has had the opposite effect in later years: many fans, especially outside of Japan, only know the ''Dr. Slump'' cast because of their guest spot on ''Dragon Ball''. It's gotten to the point that Arale's made it into at least three Dragon Ball video games as a playable character! ''Budokai Tenkaichi 3'', ''Origins'' and ''Revenge of King Piccolo'', to be precise. The first one also caused a good amount of rejoicing for those who knew her.
* The canons of ''VisualNovel/{{Tsukihime}}'', ''VisualNovel/FateStayNight'' (plus others) are generally grouped together and called the NasuVerse. There's rarely direct crossover of the characters, except in [[BattleMoonWars spin-off]] [[VideoGame/MeltyBlood games]] and non-canon side-comics. WordOfGod on each canon's characters respective power levels in relation to each other ([[MemeticMutation can Shiki kill Servants?]]) is [[FlipFlopOfGod conflicting]]. Even better: it is canon in the series that alternate timelines exist in which different events took place, and that travel between them is possible (albeit ''extremely'' difficult, this being the Second Magic), so it can be said that ''all'' routes of ''all'' materials are canon in one universe or another.
** Except ''Literature/KaraNoKyoukai'' which, by WordOfGod, explicitly isn't in the same universe as Tsukihime.
* LeijiMatsumoto is notorious for this, with ''GalaxyExpress999'', ''CaptainHarlock'', ''QueenMillennium'', and ''SpaceCruiserYamato'' crossing over to various degrees, not always following a consistent continuity.
* Endings of ''GetterRobo Armageddon'' and ''New Getter Robo'' [[spoiler: in which Armageddon versions of Ryoma, Hayato and Benkei and New version of Ryoma ends in WarriorHeaven, alongside countless Getters, fighting unknown monsters]] has hinted that all Getter's separated continuities (two mentioned above, KenIshikawa's manga continuity, ''Getter Robo DASH'' manga and anime ''Getter Robo Go'' and ''Shin Getter Robo Vs Neo Getter Robo'') might exist in the same Multiverse.
* Madhouse Studios anime adaptations of four MarvelComics' titles - ComicBook/{{X-Men}}, ComicBook/IronMan, ComicBook/{{Wolverine}} and ComicBook/{{Blade}} - are set in one Universe, confirmed both by WordOfGod from Marvel and the same Wolverine appearing in all four anime.
* GaoGaiGar FINAL has blink-and-you'll-miss-it cameos of characters from {{Betterman}}, establishing those two series takes place in one Universe.
* RedLine does this by making main characters from two different anime - Miki and Todoroki from ''MoleBrothers'' and Trava and Shinkai from ''TravaFirstPlanet'' - participating in the eponymous race.
* Several years ago, Hidenori Kusaka and Satoshi Yamamoto worked on a short ''VideoGame/PokemonRanger'' manga that was only released online. As it turns out in the Platinum arc of ''Manga/PokemonSpecial'', the events that occured in that online comic are indeed canon.
[[/folder]]

[[folder:Comic Books]]
* JackKirby is the TropeCodifier.
* The [[Franchise/TheDCU DC]] and [[Franchise/MarvelUniverse Marvel]] universes were born from this trope; originally, the titles published by each company did not overlap, but over time, cameos, {{Crossover}}s, and inside references combined to form the comic books into one big, interconnected web. That's not even counting the Amalgam universe.
** Mind, Marvel started this with the first issue of ''{{Spider-Man}}''. And even before that, Marvel started this 21 years earlier in the Timely Comics era, when Human Torch faced off against {{Namor}} the Submariner for the first time. They teamed a few more times over the next few years, and some of the less prominent characters occasionally got involved. Then, in 1946, Timely launched the All-Winners Squad, teaming up existing characters like ComicBook/CaptainAmerica, the Human Torch, and the Sub-Mariner (among others)
** DC started it twenty years earlier in All-Star Comics #3 with the Justice Society's first meeting. To this day, it's generally accepted that the Justice Society is the first-ever example of a super hero team lasting longer than a single issue in comics history.
** DC has also historically made a habit of assimilating the characters of other comics companies into their multiverse - Quality Comics (Uncle Sam and the Comicbook/FreedomFighters, ComicBook/PlasticMan, Comicbook/{{Blackhawk}}), Creator/FawcettComics ([[ComicBook/{{Shazam}} Shazam, Captain Marvel and the Marvel Family]]), Creator/CharltonComics (CaptainAtom, ComicBook/BlueBeetle, TheQuestion), WildStorm Comics (TheAuthority, WildCATS), Creator/MilestoneComics (ComicBook/{{Icon}}, ComicBook/{{Hardware}}, ComicBook/{{Static}}) and Franchise/ArchieComics' Red Circle superhero characters. Generally, these characters start off in alternate timelines, and then some sort of universal crisis reboots the DC Universe yet again, merging the timelines.
* ''{{Shazam}}'' and ''Kid Eternity'' are a particularly interesting example. DC acquired the rights to both from separate comic companies. Eventually, they realized that ''Shazam'''s Freddy Freeman and the [[NoNameGiven nameless]] Kid had remarkably similar back stories--both were [[RaisedByGrandparents raised by a grandfather]] who died in a boating accident, which also resulted in the grandson getting superpowers. The obvious solution? [[SuddenNameChange Name the Kid]] Kit Freeman and reveal that he and Freddy are brothers.
* ''ImageComics'' is an interesting case. Originally, all of its titles took place in a shared universe. Over time, the original Image partners focused on their own corners of the Image Universe, causing the continuity to split into several distinct sub-continuities. The ''Shattered Image'' crossover made the split official. But Image partners still occasionally "borrowed" each others' characters, so the sub-universes still interacted. As new, non-partner creators become more prominent in Image Comics, they started building universes of their own, and they occasionally used the Image partners' characters. For example:
** Characters from Jay Faerber's creator-owned series (''NobleCauses'', ''Venture'', ''Firebirds'', & ''{{Dynamo 5}}'') appear in each other's books all the time, creating a loose-knit "Faerberverse".
** Robert Kirkman's characters occasionally cross over in a similar fashion (and some times become supporting cast - especially in ''ComicBook/{{Invincible}}''). The Kirkmanverse and Faerberverse intersect at a number of points, especially The Pact mini-series. Other Image characters, such as SavageDragon and {{Shadowhawk}}, often pop up. So far, however, {{Spawn}} had yet to make an appearance. This changed with ''Image United'', which brings together characters of all of the current Image partners (Erik Larsen, Rob Liefeld, Todd [=McFarlane=], Marc Silvestri, Robert Kirkman, and Jim Valentino), as well as Whilce Portacio and several other creators.
** Angela from the ''Comicbook/{{Spawn}}'' universe jumped ship to the MarvelUniverse at the close of ''Comicbook/AgeOfUltron''. Though it's made clear that her home dimension exists outside the Marvel U.
* Eclipse Comics' four-part crossover mini-series, ''Total Eclipse'' brought together virtually all company-owned and creator-owned characters that the company published.
* The ''Harlem Heroes'' strip in ''ComicBook/TwoThousandAD'' (about a basketball team with jetpacks in 2050) appeared to be totally unconnected to the 22nd centuy of the ''ComicBook/JudgeDredd'' universe until the son of one of the Heroes (John "Giant" Clay) joined the Judges (as Judge Giant). The ''ComicBook/JudgeDredd'' story "Hammerstein" suggested ''ABC Warriors'' was also set in the past of the Dreddverse, but later ''ABC Warriors'' stories contradicted this.
** Dredd has also had crossovers with other ''2000 AD'' strips whenever the writers felt like it, most notably ''StrontiumDog'' and the story Helter Skelter (where GarthEnnis basically crossed ALL his favourite strips over with Dredd).
** Meanwhile, ''2000 AD'' stalwart Pat Mills has crossed over ''everything he's ever written for 2000 AD'' with each other. Invasion!/Savage, Flesh, Ro-Busters, ABC Warriors, and ''ComicBook/NemesisTheWarlock'' all slot together.
** Ian Edginton does the same thing with his ''2000 AD'' strips: both ''Stickleback'' and ''The Red Seas'' share a secret organisation, little mentions and character cameos abound, and the same brand of monster appears in ''Stickleback'', ''Ampney Crucis Investigates'', and ''Detonator X''.
*** Even more Edginton crossovers: Sir William Ashbless, [[spoiler: immortal]] designer of the titular ship in ''Leviathan'' made a cameo appearance in ''Stickleback'' and his shipping company, White Hart Line, got name dropped in ''Ampney Crucis Investigates.'' Also a few locations have been repeated across the various strips at different periods in history.
** John Smith did a similar thing from the start in order to make his stories stand out: all his initial ''Future Shocks'' linked in to an organisation called Indigo Prime, and a couple of Indigo Prime agents also appeared in ''Tyranny Rex''. Indigo Prime then got its own series, and eventually crossed over with Smith's Creator/DCComics series, ''Scarab''.
* Creator/AlanMoore, as time has gone on, has turned ''ComicBook/LeagueOfExtraordinaryGentlemen'' into this, making vague references to the source material for ''Ozymandias'' and ''The Black Freighter''. Oh, sure, it's only references to the inspirations for them, and Moore would probably rather have his skin boiled than actually go further than that, but this is Creator/AlanMoore, ''there are no coincidences''.
** That's a bit of an odd example, since the League already existed in a world where [[AllMythsAreTrue all and we mean really ALL myths are true]]. Volumes one and two of the ''ComicBook/LeagueOfExtraordinaryGentlemen'' comics were entirely populated by {{Historical Domain Character}}s, so a few characters created by the author is only a very small step further.
** As an aside, Moore is a close friend to Moorcock, close enough that Moorcock has allowed Moore to put in some Moorcock characters into the ''League'' series free of charge.
* FrankMiller's Franchise/{{Batman}} stories: ''Comicbook/BatmanTheDarkKnightReturns,'' ''ComicBook/BatmanYearOne,'' ''TheDarkKnightStrikesAgain,'' and ''[[ComicBook/AllStarBatmanAndRobinTheBoyWonder All-Star Batman and Robin]]'' were originally supposed to be in separate universes, with only ''Comicbook/BatmanTheDarkKnightReturns'' and ''TheDarkKnightStrikesAgain'' having any clear continuity with each other. With the restoration of the DC [[TheMultiverse Multiverse,]] all of the FrankMiller-penned Batman stories are now set in Earth-31.
* [[http://www.bleedingcool.com/2009/10/01/the-mark-millar-tie-up-athon-spoilers/ This article]] suggests that all of MarkMillar's later Marvel works (''1985'', ''ComicBook/FantasticFour'', ''KickAss'', and ''OldManLogan'') is all interconnected. (Three of those are automatically canon to each other anyway, of course, but ''Kick Ass'' is more of a surprise.)
** Even ealier Millar estabilished connections between three comics published by different companies - ''ComicBook/{{Wanted}}'', ''{{Chosen}}'' and ''ComicBook/TheUnfunnies''. The reason why at the end of the ''Chosen'' [[spoiler: media doesn't report Antichrist's miracles is that they're controlled by supervillains from ''Wanted'']]. And Troy Hicks from ''Unfunnies'' [[spoiler: helped Satan rape Antichrist]]. Never published ''Run!'' was supposed to be set in that world too.
* Creator/GrantMorrison's ''ComicBook/AllStarSuperman'' and ''ComicBook/DCOneMillion'' seemed to be tied in the same continuity.
** Of course, GrantMorrison is one of the architects of [[http://www.hyperborea.org/flash/hypertime.html Hypertime]] (the other being Mark Waid) which posits that it is all true. Under this concept, the events of ''DC vs. Marvel'' exists somewhere in continuity.
** Almost all of Morrison's DC works are tied to each other, ''as well to the [[RealLife real world]]'', forming a big "Morrisonverse". Here's how it goes: In ''All-Star Superman'' Superman creates the infant universe Qwewq. In ''[[JusticeLeagueOfAmerica JLA]]'' we see the heroes discover (a version of) Qwewq. Both in ''ASS'' and in ''JLA: Confidential'' we see that Qwewq actually contains "our" Earth, i.e. a realistic Earth with no superheroes. The final Morrison-penned issues of ''Comicbook/DoomPatrol'' and ''Comicbook/AnimalMan'' take place in a realistic world with no superheroes (and they both share the same colour scheme, meaning it's the same world in both), which is presumably Qwewq, i.e. "our" world. In ''SevenSoldiers'' we find out the ultimate fate of Qwewq (or at least one version of it). ''FinalCrisis'' (which takes place in the same universe as ''JLA'') refers to Bleed (the "sea" that separates different universes in the DC multiverse) as "ultramenstruum", and the same term is used is ''Comicbook/TheInvisibles'', implying that the Invisibles universe is a part of the larger DC multiverse. If we accept that Qwewq is "our" universe, this means our universe exists inside a larger universe populated by superheroes. Both ''Comicbook/FlexMentallo'' and ''ComicBook/TheFilth'' feature the "real" world to which superheroes from outside this world burst in; thus, the real world in both these comics could be (a version of) Qwewq. And then a huge chunk of the [[Franchise/{{Batman}} Damian Wayne]] stories written by Morrison that take place in the [[TwentyMinutesIntoTheFuture not too distant future]] were revealed to be set in the past of ComicBook/DCOneMillion and ends with Damian training Terry [=McGinnis=] from WesternAnimation/BatmanBeyond to become his successor. Lastly it also seems that DC One Million takes place in the future of All Star Superman as Solaris and Kal Kent appear and happens to be the story of how Superman ended up having to fix the sun. To sum it up, almost all of Morrison's major works for DC are welded together, though admittedly some of the links between them are vague.
* When Semic Comics, a French comic publisher, decided to revive the characters it inherited from defunct ''Editions Lug'', editor Jean-Marc Lofficier set out to link over 2000 largely unrelated characters from just about every comic book genre into a single continuity. Some characters had to be revamped fairly drastically to fit in, and a few had to be revamped to avoid duplication.
* In ''ComicStrip/NonSequitur'', Wiley frequently used four separate sets of recurring, originally nameless, characters: a silent {{Everyman}} who'd observe some of the comics' less absurdist strips, a ''VideoGame/LeisureSuitLarry''-ish barfly, a snarky BrattyHalfPint girl and the Sunday-only diner owner "Offshore" Flo (and her tall-tale telling patron, Eddie). Gradually, the characters started interacting: the Everyman and the barfly were seen hanging out at the bar, the girl and Flo would occasionally be seen reacting to something from the Everyman's radio talk show. Eventually, Wiley brought all these elements together to form a central cor: Joe (the everyman) and Bob (the barfly) are brothers, Danae (the little girl) and her little sister are Joe's daughters and Flo is Joe and Bob's mother. Eddie remains "just" Eddie.
* In one Super Special ''ComicBook/ArchieComicsSonicTheHedgehog'', Sonic finds himself universe hopping to the WesternAnimation/SonicUnderground universe. In the 25 Years Later storyline, he names his children after his counterpart's siblings.
** In the same Super Special, Sonic and Sally end up universe hopping again and teaming up with ComicBook/SabrinaTheTeenageWitch, making the Sonic comics part of the Archie Comics multiverse, not just under their label.
** In another, the Freedom Fighters universe hop into the Image Comics universe, meeting Spawn, Savage Dragon, the Maxx, and Shadow Hawk.
** [[ComicBook/SonicTheHedgehogMegaManWorldsCollide The Mega Man comic Started being welded into the Sonic comic canon as well.]]
[[/folder]]

[[folder:Film]]
* Present in horror films long, long before ''Film/FreddyVsJason''. In the UniversalHorror series, ''Film/FrankensteinMeetsTheWolfMan'' triggered the tendency to pile on the monsters, insisting that Dracula, the Wolf Man and Frankenstein's Monster all existed in a common universe. This does not work well with continuity (''Film/TheWolfMan1941'' takes place in the present day while the others happen in a dimly-characterized past), but they didn't care much by that point (Universal's horror films of the 40s are strikingly dumber and more juvenile than those of the 30s).
* Predating even these examples: Fritz Lang's ''DasTestamentDesDoktorMabuse'' (1933). Nominally a sequel to Lang's ''DrMabuseTheGambler'' (1922), it also incorporates Inspector Lohmann from ''{{M}}'' (1931) as the main protagonist. Blending the super villain from a pulp thriller with the hero of a police procedural works surprisingly well. Well enough that a 1960s revival of the Mabuse series retains Lohmann as its protagonist.
* Creator/QuentinTarantino has created a largely common universe of his films by including subtle crossreferences (for instance, characters commonly refer to others; Mr. White mentions Alabama and Mr. Blonde has Scagnetti as a parole officer, Vic Vega and Vincent Vega are brothers, etc.) and cameos, but he says that his movies are divided into ''two'' universes.
** The first is an [[spoiler: alternate reality where Hitler was shot down in a theater causing Americans to be obsessed with pop culture and extremely violent]], which consists of ''Film/PulpFiction'', ''Film/ReservoirDogs'', ''Film/TrueRomance'', ''Film/InglouriousBasterds'', ''Film/DeathProof'' and possibly ''Film/DjangoUnchained''.
** The second is a universe that takes place in Tarantino movies that are supposedly released in both the real world and the main Quentin Tarantino Universe, which consists of ''Film/KillBill, Film/FromDuskTillDawn, Film/NaturalBornKillers'', and possibly ''Film/{{Machete}}'' and ''Film/PlanetTerror'' because of cameos of Earl and Edgar Mcgraw in both movies. Interestingly, the title character in ''Film/{{Machete}}'' appears in another of Creator/RobertRodriguez's films...''Film/SpyKids''.
** Tarantino has also stated that Django and his wife Broomhilda are intended to be the ancestors of [[Film/{{Shaft}} John Shaft]].
* In all honesty ''Franchise/{{Alien}}'' and ''Franchise/{{Predator}}'' were never really meant to part of the same universe. The Xenomorph head seen near the end of ''Film/{{Predator 2}}'' was only meant as a joke but inspired dozens of video games and comic books until the connection was made completely canon in the ''Film/AlienVsPredator'' movies. Hints placed by Creator/RidleyScott in ''Film/{{Prometheus}}'' and in the latest re-edit of ''Film/BladeRunner'' suggest that they (and of course the rest of the ''Film/{{Alien}}'' franchise, and transitively ''Franchise/{{Predator}})'' share the same continuity.
* Any {{Kaiju}} film made by made by Creator/{{Toho}} is prone to become part of the ''Franchise/{{Godzilla}}'' universe. In fact some of Godzilla's most recognized enemies came from their own movies, including Film/{{Mothra}} and Film/{{Rodan}}. Even the [[Film/{{Godzilla 1998}} 1998 version of Godzilla]] is canon due to him getting his butt whooped by the real Godzilla in ''[[Film/GodzillaFinalWars Final Wars]]''.
** Before ''Final Wars'', in ''Film/GodzillaMothraKingGhidorahGiantMonstersAllOutAttack'' (aka ''GMK''), there's another acknowledgment of the US ''Godzilla'' that works even better at integrating it into canon. In this film's continuity, Godzilla hasn't been seen since [[Film/{{Gojira}} the original 1954 attack on Tokyo]], and many people no longer remember what he looked like. It's said that there was a reported Godzilla attack in New York a few years earlier, but it's unconfirmed whether it was the real Godzilla. This fits perfectly with the US film, wherein Japanese characters identify the creature as "Gojira." Indeed, ''GMK'' has characters mistaking another monster (Baragon) for Godzilla, which may be an intentional retcon for how the creature in the US film got misidentified that way.
** In an interesting note that there is a Toho version of Film/KingKong existed in the Godzilla universe that first appeared in ''Film/KingKongVSGodzilla'' and later got his own movie called ''Film/KingKongEscapes''. The Toho version of King Kong was a very altered version though considering that he had more raw power, was intelligent enough to learn and adapt to situations, and lived on Mondo Island instead of Skull Island. [[RuleOfCool Oh and he was able to draw power from electricity]].
[[/folder]]

[[folder:Literature]]
* Fantasy author MichaelMoorcock gradually connected almost every single character he'd created into a MythArc revolving around the concept of the [[CosmicPlaything Eternal Champion]]. Indeed, this article was originally titled "The Moorcock Effect" in reference to him.
** Moorcock's Series/DoctorWho novel ''The Coming of the Terraphiles'' features a ''Captain'' Cornelius, who may or may not be another aspect of the Eternal Champion (much like JerryCornelius) which ties the Eternal Champion into the Whoniverse as well! There's also a Second Aether, referencing Moorcock's Second Ether sequence which also takes place in the Eternal Champion continuity.
* In the 1980s, Creator/IsaacAsimov wrote a series of novels that linked his ''Robots'', ''Empire'', and ''{{Foundation}}'' novels into a single continuity. He also even went so far as to in ''Foundation and Earth'' suggest (via throwaway reference in dialogue) a tenuous connection between the Robots/Empire/Foundation series and an otherwise seemingly unrelated, comparatively obscure time-travel novel, ''Literature/TheEndOfEternity'', which he wrote in the 1950s (interestingly enough, if they ''were'' in the same continuity, the end of the novel would effectively have caused the ''entirety of the events in the rest of the series'', because said ending [[spoiler:revolves partly around allowing humanity to expand into space instead of mouldering on Earth]]).
** Don't forget throwing in a reference to his standalone novel Nemesis in one of the later Foundation books, despite the fact that Nemesis and the Robots/Empire/Foundation books taking place in the same universe makes no sense whatsoever (not even the space-travel physics work the same way). Though it may have been a literal reference to his ''novel''.
** The officially licensed FanSequel, ''Psychohistorical Crisis'' {{retcon}}s a number of aspects of the Foundation series, and also ties in Asimov's otherwise unrelated short story ''Literature/{{Nightfall}}''.
* The final novels in AnneRice's ''VampireChronicles'' tie Lestat's story into that of TheMayfairWitches.
** Actually, they were tied together much before that, notably by the Talamasca (introduced in ''Queen of the Damned'' and later a key player in both the vampires and witches novels) and a few common supporting characters like Aaron Lightner. In other words, the Witches novels avowedly take place in the same world as the ''Vampire Chronicles'' from day one, though their interactions increase substantially over time. Hints in ''The Vampire Lestat'' also indicate that Rice's least-liked novel, ''The Mummy,'' also shares a continuity with these series.
** The novel ''The Queen of the Damned'' establishes that witches and spirits are real. ''Memnoch the Devil'' claims that God, the angels, and TheDevil are all real.
* Creator/JRRTolkien:
** ''Literature/TheHobbit'' was not, at the time of its writing, intended to be in the same continuity as ''Literature/TheSilmarillion'', which Tolkien regarded mainly as personal recreation and had as yet no intent of publishing. Despite this, he couldn't help throwing in a few [[ShoutOut names and locations]] that referenced ''The Silmarillion''. When he began writing the sequel that would become ''Literature/TheLordOfTheRings'', he went whole-hog and moved ''The Hobbit'' to Middle-Earth, ''The Silmarillion'' becoming the BackStory of the novels. In fact, the ring that Bilbo found was originally just an ordinary, harmless magic ring and nothing more, and Gollum, having no motive to kill Bilbo, happily led him to safety at the conclusion of the riddle game. It wasn't until ''The Lord of the Rings'' was being written that Tolkien decided that it was ''the'' ring, and he altered the Bilbo/Gollum encounter to be a little more sinister. The in-universe explanation for the altered narrative is that Bilbo wrote the first version while under the influence of the ring as he wanted to conceal the actual circumstances of his acquiring it, while the revised, true version was written later, after he was no longer in the ring's grasp.
** Tom Bombadil, Goldberry and Old Man Willow originally appeared in a poem published in 1933. They had no connection to Middle-Earth until the writing of ''Literature/TheLordOfTheRings'' was in progress, and that didn't turn them into anything more significant than a WackyWaysideTribe.
* Creator/RobertAHeinlein did this towards the end of his career, incorporating all his previous stories (often with radically different universes) into one meta-universe, thanks to a handy trans-dimensional device invented by one of his characters. Then he brought the ''JohnCarterOfMars'' series in, and the [[Literature/LandOfOz Oz books]], and eventually ''[[http://en.wikipedia.org/wiki/World_as_Myth all fiction ever created]]''.
** Though he did give preference to the ones he liked, and especially those written by authors with whom he was personally acquainted; one of the transdimensional 'jumps' involved taking the characters into the Literature/{{Lensman}} universe created by his friend, Creator/EEDocSmith.
*** He even threw in some real people: the characters of ''Literature/TheNumberOfTheBeast'' run into [[Creator/LewisCarroll Charles Dodgson]] while in Wonderland, and near the end of the novel, it's mentioned that [[Creator/RobertAHeinlein Bob]], [[Creator/ArthurCClarke Arthur]], and [[Creator/IsaacAsimov Isaac]] should be showing up for a big meeting soon.
** Nearly all main characters he ever wrote are in one scene at the end of ''Literature/TheCatWhoWalksThroughWalls''.They try to [[spoiler:recover Mycroft Holmes, whose death was perhaps the biggest TearJerker Heinline ever wrote. Towards the end the characters are aware they are in a story, and find the Author to be a bastard...]]
* Creator/LarryNiven originally had two continuities: the first was the "slowboat" stories of early colonization of space by humanity (featuring the novels "World of Ptaavs", the Gil Hamilton stories, and "A Gift From Earth"), while the second featured faster-than-light travel and aliens (featuring the stories of Beowulf Shaeffer, Louis Wu, and the ''Literature/{{Ringworld}}''. And then he wrote his short story "Relic of Empire", which combined the two continuities and created the ''Literature/KnownSpace'' universe.
* The first novel in Creator/TerryPratchett's ''Literature/NomesTrilogy'', ''Literature/{{Truckers}}'', takes place in the (real) town of Grimethorpe, but in the later books the Store is relocated to Blackbury, which is also the setting of the Literature/JohnnyMaxwellTrilogy.
* Creator/EdgarRiceBurroughs did this when Literature/{{Tarzan}} first traveled to the underground world of Literature/{{Pellucidar}} to rescue that title's hero. It grew from there under his pen and under the pen of others using his characters.
** There was a series of action figures: "Tarzan on Mars". Of course, poor Edgar had nothing to do with it.
** In ''A Fighting Man of Mars'', Jason Gridley appears. Since Gridley met Tarzan in Tarzan At the Earth's Core, a Pellucidar novel, this links Tarzan, Barsoom, and Pellucidar.
*** Gridley is also mentioned in the Amtor (Venus) series, linking those five books as well.
*** Tarzan is mentioned by the narrator as having participated in some historical event prior to the main story of the first story. Even then, the Tarzan books, and by association, everything Tarzan had appeared in, were part of the Amtor universe within the first twenty five pages of Pirates of Venus.
**** Also, the technology for the Moon mission from ''The Moon Men'' was Barsoomian in origin.
*** And Tarzan is a supporting character in ''The Eternal Lover'', whose central character is the sister of the hero of ''The Mad King''; thereby bringing those otherwise non-series novels into the fold.
* Terry Brooks' ''Literature/{{Shannara}}'' series was always established as being set a fantasy world that formed AfterTheEnd of modern civilisation. The ''Genesis of Shannara'' series is set during the collapse of civilisation, and establishes the past of the Four Lands as the UrbanFantasy setting of his ''Literature/TheWordAndTheVoid'' novels.
* What AugustDerleth called the "CthulhuMythos" (a term never used by HPLovecraft and only by Derleth after Lovecraft's death) originated from cross-references by Lovecraft between his own stories and that by other writers. He (Lovecraft, not Derleth) Lovecraft referenced passages from the Necronomicon, other forbidden books, or placing offhand comments during the expository monologues, about various {{Eldritch Abomination}}s that have no bearing on the current story. Specifically, ''The Dream-Quest of Unknown Kadath'' ties most of his early standalone [[ShortStory short stories]] into the Dreamlands Cycle, and also brings in ''Pickman's Model'' and the Randolph Carter stories. At the end, the Dreamlands Cycle is linked to the so-called CthulhuMythos, though a few stories (such as the early "Dagon") ''may'' be outside the grand continuity. Several other authors have tied them together, notably AugustDerleth and Creator/ClarkAshtonSmith. Even the demonic race beneath the Earth from "The Rats in the Walls" seems to be referenced in "The Whisperer in Darkness".
* Creator/ClarkAshtonSmith's Xiccarph and Zothique series were not originally connected to the "mythos" in Smith's own writings.
* Lovecraft and others tied works by earlier writers he did not personally know. Examples: Creator/RWChambers' ''TheKingInYellow'' (referenced in "The Whisperer in Darkness"), to the work Creator/ArthurMachen (a mention of the Aklo language) and LordDunsany (Bethmoora).
* Beginning with ''Literature/{{It}}'', Stephen King began tying many of his novels into ''Franchise/TheDarkTower'' series, to the point that every single novel he wrote during the early 2000s was somehow related to the epic. The process included bringing back a character he PutOnABus (literally) in ''Literature/SalemsLot'' and {{retcon}}ning the BigBad from ''Literature/TheStand'' into the Crimson King's [[TheDragon Dragon]]. (Indeed, the Crimson King himself made his first appearance outside ''The Dark Tower'' series.)\\\
From ''Literature/{{Desperation}}'' (1996) to ''Literature/FromABuick8'' and ''Everything's Eventual'' (2002), 100% of King's fiction output (six novels and two story collections) tied into ''Franchise/TheDarkTower'' (at least retroactively). These were bookended by ''Literature/WizardAndGlass'' in 1997 and the conclusion of ''The Dark Tower'' series in 2003-04. Plus the aforementioned incorporation of everything back to ''Salem's Lot'' and ''Literature/TheStand'', written before ''Literature/TheGunslinger''.\\\
And lest we forget, '''Salem's Lot'' takes place in the same city as ''Jerusalem's Lot'', an earlier short story, confirmed to be in the CthulhuMythos. Therefore, ''The Dark Tower'' series is part of the Mythos by extension. Oh and as mentioned above {{Transformers}}, Series/DoctorWho, Franchise/SherlockHolmes, and pretty much everything else on this page has crossed over with the Cthulhu Mythos.
** It's also been established that if there's anyone in a King story with the initials R.F., they're probably a very particular person: [[spoiler: Randall Flagg, the BigBad of ''Literature/TheStand'', The Eyes of the Dragon (as Flagg, no first name), and the Crimson King's [[TheDragon Dragon]].]] Except for (presumably) Rudy Foggia of ''The Jaunt'', who is quite dead at the beginning of the story.
** ''Literature/{{It}}'' also contains an appearance by Charles Pickman, from the Creator/HPLovecraft story ''Pickman's Model'' -- which ties it to all the Lovecraft stories mentioned below. King's next novel, ''TheTommyknockers'', not only crossed over with ''It'', but also tied in several of King's other novels, including ''Firestarter'' and ''Literature/TheTalisman''.
** Also, the books ''Dolores Claiborne'' and ''Gerald's Game'' refer to each other as the female protagonists of the books have a psychic link, having times when they suddenly get the feeling that this other person, who they don't know, is somehow in danger.
** ''Literature/{{Misery}}'' refers to ''Literature/TheShining'' at one point, when Annie mentions the ruin of the Overlook Hotel.
* Tony Hillerman once had two series, one featuring Navajo cop Jim Chee and one featuring Navajo cop Joe Leaphorn. There is now only the Leaphorn & Chee Mysteries.
** Though to be fair, from the beginning the Chee stories (which came second) would reference Leaphorn and characters and events from his stories--they just weren't featured in the same books for a while.
* First ''The Poet'' and ''Blood Work'' got sucked into MichaelConnelly's Harry Bosch universe, now ''Void Moon'' has been caught in the gravity well, too. Of course, unlike many of the other entries here, Harry Bosch's "world" is that of LAPD Homicide, and so referencing or including a few of Michael Connelly's stand alone novels doesn't really require much in the way of a {{Retcon}}.
* Before he's done, F. Paul Wilson's ''Adversary Cycle'' bids fair to weave in practically every book and short story the man has ever written.
* Creator/MercedesLackey's assorted UrbanFantasy stories seem to be set in different continuities, until mention is made of the west coast elfhames (from the ''Bedlam's Bard'' series) in the ''Literature/{{SERRAted Edge}}'' novels, and of Tannim, the mulleted protagonist of the [=SERRAted=] Edge novels appearing as a bit character in his teens in ''Jinx High'', a Diana Tregarde investigation.
** Since ''Jinx High'' was Tannim's first appearance, and the ''Bedlam's Bard'' events were namechecked in the first [=SERRAted=] Edge novel, this one was evidently intended from the start, or nearly so.
* Kate Elliott has confirmed that her new ''Crossroads'' trilogy of fantasy novels is actually a fictional story within the context of her earlier ''[[Literature/NovelsOfTheJaran Jaran]]'' series of SF novels.
* PeterFHamilton retconned several of his earlier SF short stories to be set in the same universe as his immense, later ''NightsDawn'' Trilogy and published them in a collection called ''A Second Chance at Eden''. However, he has avoided this phenomenon elsewhere and has created no less than three distinct SF universes existed at similar points in history, making it impossible for them to coexist in the same continuity.
* Creator/AlastairReynolds did something similar with several of his early SF short stories, retrofitting them into his ''[[Literature/RevelationSpaceSeries Revelation Space]]'' series of books and publishing the results as a collection called ''Galactic North''.
* Creator/GuyGavrielKay's ''Literature/TheFionavarTapestry'' presents the world of Fionavar as so significant that echoes of it appear in the mythologies of every other world in TheMultiverse. His subsequent stand-alone novels ''Literature/{{Tigana}}'' and ''Literature/TheLionsOfAlRassan'', although each set in a different world, each has a moment showing that to be true. ''Literature/{{Ysabel}}'' is more overt, actually featuring several characters from the ''Fionavar Tapestry'' later on.
* The PeterDavid novel ''Howling Mad'' mentions Mayor Penn, who is the returned King Arthur from ''Knight Life''.
* A particularly confusing example is ''The Well of Lost Plots'', which ties the world of ''Literature/ThursdayNext'' into a book ([[NurseryCrime now a series]]) that Jasper Fforde wrote ''first'', but which was published ''afterwards'' (''The Big Over Easy'', originally ''Nursery Crimes''), and does so by establishing it as fictional within the Nextiverse, although, like all works of fiction, Thursday can enter it, and spends most of the book inside it, being ultimately responsible for its odd mix of genres. Everyone follow that?
** To further confuse things, the ''Thursday Next'' stories are themselves fictional within the ''Nursery Crimes'' series.
* Creator/AgathaChristie's AuthorAvatar Ariadne Oliver seems to tie several of her series together. She originally appeared in the Parker Pyne stories (as did Miss Lemon). Then she became established as a HerculePoirot character, starting with ''Cards On The Table'' (which also featured Superintendent Battle, who'd previously appeared in the two novels starring Bundle Brent). Then she was the main character in the 1961 novel ''The Pale Horse'', which also featured the vicar's wife from the ''Literature/MissMarple'' novel ''The Moving Finger''. And in ''Murder In Three Acts'', Poirot meets Mr Satterthwaite, who previously appeared in ''The Mysterious Mr Quin'' collection of short stories. Literature/TommyAndTuppence are also linked, since the same slightly unhinged old lady appears in ''The Pale Horse'', the ''Literature/MissMarple novel'' ''The Sleeping Murder'', and the Tommy and Tuppence novel ''By the Pricking of my Thumbs'', despite ''Partners in Crime'' having them refer to Poirot as a fictional character.
** Tommy and Tuppence can also be linked to the others through a mysterious character who is only referred to as Mr. Robinson. This character appears with Poirot in ''Cat Among the Pigeons'', Marple in ''At Bertram's Hotel'', and Tommy and Tuppence in ''Postern of Fate''. He also appears in ''Passenger to Frankfurt'', which does not feature any of Christie's series detectives.
* While Creator/KimNewman has seeded connections between his books since the beginning, the short story "Cold Snap" seems to be a concentrated effort to tie them ''all'' together. A "Literature/DiogenesClub" story (and therefore featuring characters whose AlternateUniverse selves appear in the ''Literature/AnnoDracula'' novels) it adds characters from his early work such as ''Jago'', and even features the villain from his ''Series/DoctorWho'' novella ''Time And Relative''.
** Under the pseudonym Jack Yeovil, Newman wrote a number of books based on Games Workshop properties. ''Krokodil Tears'', one of the ''Literature/DarkFuture'' books, had its BigBad have a vision of an alternate version of himself as the Big Bad from his Vampire Genevieve series of ''Warhammer'' books.
* Creator/KimNewman isn't the only author to tie his personal {{Verse}} into the {{Whoniverse}}. Iris Wildthyme was a character in Paul Magrs' MagicRealism novels, before he revealed she was an extremely eccentric Time Lady.
** Iris Wildthyme, in her appearances in novels and audios, occasionally interacts with an organisation called MIAOW, The Ministry for Incursions And Other Wonders (simultaneously a parody of ''Series/{{Torchwood}}'' and ''Series/DoctorWho'''s UNIT). This organisation has also turned up in his Brenda and Effie series of novels set around Whitby. Charaters from his Literature/EighthDoctorAdventures novel ''Mad Dogs and Englishmen'', his AudioPlay/BigFinishDoctorWho audio drama ''The Boy That Time Forgot'', and the ''Pheonix Court'' series that featured the original version of Iris have also appeared in this series. A character from one of Magrs' Tenth Doctor novels also reappeared in an Iris Wildthyme short story, along with a character from the Brenda and Effie series.
* Creator/HRiderHaggard's novel ''She and Allan'' brought together Ayesha from ''Literature/{{She}}'' and Allan Quatermain from ''Literature/KingSolomonsMines''.
* Creator/EEDocSmith's ''Literature/{{Lensman}}'' series of novels was originally 4 books long (initially published in serial form in an SF magazine). In the late 1940s or early 1950s, he took an early work of his named ''Triplanetary'' and retrofit it in with the rest of the ''Literature/{{Lensman}}'' universe. He wrote an additional novel, ''First Lensman'', to bridge the gap between the two storylines.
* Creator/JulesVerne connected ''TheMysteriousIsland'' with his earlier books ''Literature/TwentyThousandLeaguesUnderTheSea'' and ''Literature/InSearchOfTheCastaways'' by adding Captain Nemo from the former and Tom Ayrton from the latter to the cast of characters; however it opened a few [[PlotHole plot holes]], not to mention that the time period doesn't match.
* Creator/DavidGemmell has stated that all his books take place in the same world, despite covering vastly different territory, such as a low-magic fairly standard fantasy world (''DrenaiTales''), a post-apocalyptic world (''The Jerusalem Man'') and our own world (an Arthurian duology and a duology set in ancient Greece).
* L. Frank Baum, the author of ''Literature/TheWonderfulWizardOfOz'', also wrote [[Literature/LandOfOz Oz sequels]] and non-Oz works of fantasy. Through several {{Crossover}}s, he established that all of them take place in the same magical continent, called Nonestica.
* The ninth FightingFantasy gamebook, ''Caverns of the Snow Witch'', took the player on a tour of the major locations from two of the previous books (''Warlock of Firetop Mountain'' and ''Forest of Doom''), establishing that they all took place in the same land of Allansia. (It also name-checked a character from ''Forest of Doom''.) The monster manual ''Out of the Pit'' then expanded this world: Allansia and The Old World, the setting for the ''Sorcery'' series of gamebooks, were two continents on the world of Titan.
* Many, if not ''all'', of the books written by TedDekker are in the same continuity, as one book references characters from seemingly unrelated books.
* Leslie Charteris introduced Inspector Teal in the novel Daredevil featuring Storm Arden before Teal appeared in the Saint series.
* Creator/PoulAnderson's [[Literature/PolesotechnicLeague Nicholas van Rijn stories]] and Literature/DominicFlandry stories weren't, originally, part of the same universe. But a bit of prodding by fans, and he wrote some bridging so that now they are both part of the ''Literature/TechnicHistory''.
* DaleBrown has done this. Rebecca Furness and Daren Mace, characters originally in the non-Patrick [=McLanahan=] book ''Chains of Command'', joined the main continuity in ''Battle Born'' and ''Warrior Class'' respectively. The eponymous space station of ''Silver Tower'', thought a victim of CanonDiscontinuity because of its long absence from his books, joins the main continuity in ''Strike Force''. TheDragon of non-Patrick [=McLanahan=] book ''Storming Heaven'', Gregory Townsend, is DragonAscendant BigBad of main continuity title ''The Tin Man''.
* Creator/IainBanks, in his mainstream (non-SF) literature has said he doesn't do sequels/prequels; though he did include one subtle crossover in ''Complicity'': Cameron's friend Al, an engineer he met on a paintballing weekend, is Alexander Lennox, recovered from his car-crash in ''The Bridge''.
* All of Creator/ChristopherMoore's varied books appear to take place in the same verse, whether the setting is modern suburban California or Israel in Jesus's time. Various characters make appearances outside of their respective novels, like angels and vampires and fruit bats. Of course, whether this is actual canon ''welding'' or just his [[TheVerse Verse]] depends on whether Moore had the broad strokes sketched out from the start or just made it up as he went (and tied it together afterwards)!
* Creator/PhilipJoseFarmer took this to the extreme in his creation of the Wold Newton Universe. His novels ''Tarzan Alive'' and ''Doc Savage: His Apocalyptic Life'' link the two heroes' respective families to the same event, the meteor strike in Wold Newton, Yorkshire, England, on December 13, 1795. Other stories, both by Farmer and other writers, have expanded the Wold Newton universe to demonstrate links to Literature/TheScarletPimpernel, Franchise/SherlockHolmes, TheSpider, Literature/JamesBond, Literature/NeroWolfe, [[Literature/TheMalteseFalcon Sam Spade]], Radio/TheLoneRanger, Franchise/TheGreenHornet, and even Franchise/StarTrek.
** In a way, his series of books beginning with ''To Your Scattered Bodies Go'' could be considered the logical conclusion of this trope, as he intentionally designed a world in which he could bring in any character from any story written by anyone.
* MadeleineLEngle first connected her "Kairos" and "Chronos" series when Canon Tallis from Kairos novel ''The Arm of the Starfish'' appears in Cronos novel ''The Young Unicorns''; several characters from each series would cross over later.
* In ''The Art of Detection'', Laurie R. King welds her wildly successful series about [[Literature/MaryRussell Sherlock Holmes' female apprentice]] to her lesser-known series about a modern San Francisco cop.
* Creator/SimonRGreen's series The {{Nightside}}, SecretHistories, and Ghostfinders take place in the same world. And constantly [[ShoutOut reference]] each other. There are also very strong connections to his Deathstalker, Forest Kingdom, and Hawk and Fisher series. And all his other writings.
** In the latest Nightside novel there's even a perspective-flipped recreation of a scene from a Hawk and Fisher novel, of the duo waiting at a tavern to meet Razor Eddie.
** Since {{Nightside}} is a CosmicHorrorStory & Urban FantasyKitchenSink set in London, it shouldn't be terribly surprising that John Taylor has had a few brushes with [[Series/DoctorWho the Wandering Doctor]].
* An [[WhatCouldHaveBeen unreleased]] series of novels (''Alien Exodus'' and ''The Human Exodus'') in the Franchise/StarWarsExpandedUniverse would have done this between ''Franchise/StarWars'', ''Film/THX1138'', and ''AmericanGraffiti''. The novel would have had descendants of the characters from the latter two works warp across time and space to ALongTimeAgoInAGalaxyFarFarAway and become the first humans in that place.
* Narita Ryohgo wrote links estabilishing that his three series of light novels - LightNovel/{{Baccano}}, Literature/{{Durarara}} and Vamp! - all take place in one Universe. For example, Shizuo from Durarara mentions getting into a fight with person strongly implied to be one of Baccano! characters.
* It's not clear if this was intended from the start, but a minor character in the Starbuck series (set in the American Civil War) by Bernard Cornwall was revealed in the second book to be the son of Richard Sharpe, the hero of the {{Sharpe}} series, Cornwall's earlier and more famous series set in the Napoleonic Wars.
* Neil Munro wrote two series of short stories for the ''Glasgow Evening News'': ''Erchie, My Droll Friend'' about a Glaswegian waiter, and ''Para Handy, Master Mariner'' about a steamboat going up the West Coast of Scotland. When Erchie needs to take a ship to his daughter's wedding, naturally it's Para Handy's ''Vital Spark''.
* Andrzej Pilipiuk has connected his Literature/JakubWedrowycz stories with his more serious trilogy called ''Kuzynki'' (''Cousins'') - Jakub is mentioned by name in second volume and makes a cameo in third, combined with the illustration to leave no doubt that this is indeed him. This is odd, because in first book of the trilogy Jakub is clearly fictional as one of the characters reads his books and considers them [[SelfDeprecation the evidence that modern Polish literature is terrible]].
* E. F. Benson's MappAndLucia series only came together with the novel of that title, which brought the characters of ''Miss Mapp'' together with those of two previous ''Lucia'' novels. Although not regarded part of the series ''per se'', another earlier novel ''Secret lives'' was also subsequently tied into the same continuity.
* AnneMcCaffrey wrote ''Pegasus In Flight'' and ''Pegasus In Space'' to officially merge the older ''To Ride Pegasus'' to ''The Rowan'' and the rest of the ''TowerAndTheHive'' series.
* Just about every book by Douglas Preston and Lincoln Child take place in the same fictional universe. They're probably best known for the Literature/AgentPendergast series, but even their non-Pendergast books share characters that tie in with one another. For example, one of their earlier books, ''Literature/{{Thunderhead}}'', introduced anthropologist Nora Kelly and featured William Smithback from their first Pendergast-related novels; Kelly was later made a recurring character in the Pendergast novels. Two Pendergast novels feature a wheelchair-bound profiler named Eli Glinn, he was introduced in an earlier novel entitled ''Literature/TheIceLimit'' and has later appeared in their new Gideon Crews series of novels. Mime, a hacker from the duo's second book ''Literature/MountDragon,'' has appeared in their later Pendergast novels.
* Several of PiersAnthony's works. The last book of the ''Mode'' series featured a brief trip to ''Literature/{{Xanth}}''. The 27th ''Xanth'' book included a visit to Phaze, a world from the ''Literature/ApprenticeAdept'' series.
* At the end of ChristopherAnvil's "War With The Outs" series, humanity learns that beyond the Outs' territory, space is controlled by two new alien races, the Stath and the Ursoids. Both of these had previously made appearances in his "Colonization" series, suggesting that the "War With The Outs" stories take place earlier in the same universe.
* Susanna Clarke published a short story where one of characters from [[{{Literature/JonathanStrangeAndMrNorrell}} Jonathan Strange And Mr. Norell]] visits village from Creator/NeilGaiman's Literature/{{Stardust}}, making both stories take place in one world. As far as we know, this is still canon.
* OlderThanRadio: French writer [[Creator/HonoreDeBalzac Honoré de Balzac]] wrote a few independant novels and short stories before making recurring characters. He next made the project of making a study of human society and called his work ''The Human Comedy'' (in reference to ''The Divine Comedy'').
* George Mann's timeline of the ''[[Literature/AffinityBridge Newbury & Hobbes]]'' universe, at the back of ''The Casebook of Newbury & Hobbes'', includes his Franchise/SherlockHolmes novel, his ''Franchise/DoctorWhoExpandedUniverse'' work and his DieselPunk TwoFistedTales of the Ghost.
* RobertEHoward did this a lot with his historical, horror and fantasy stories. Just to name a few examples: {{Kull}} was explicitly tied with ConanTheBarbarian in the essay "The Hyborian Age". Both was tied with the historical-fantasy character BranMakMorn through the Kull-Bran crossover "Kings of the Night". The ring of Thoth-Amon, from the Conan stories, and worshipers of Bran are featured in Howard's modern horror stories, while both Bran and Kull are mentioned in one of his Turlogh Dubh O'Brien stories set in 1200's. It wouldn't be unreasonable to consider all of Howard's speculative fiction to be part of [[TheVerse the same verse]], even if Howard [[AuthorExistenceFailure never lived]] to point it out himself. And of course Howard and HPLovecraft making references to each-others in their works was the foundation of the CthulhuMythos mention above.
* Members of a family named "Hempstock" have appeared in quite a few seemingly unconnected works by {{Creator/Neil Gaiman}}, including {{Literature/Stardust}}, {{Literature/The Graveyard Book}} and, most predominately, {{Literature/The Ocean at the End of the Lane}}. Death from {{ComicBook/The Sandman}} also gets a mention in Stardust.
* Indie author Royce Day's SpaceOpera ''Literature/TheRedVixenAdventures'' series and DieselPunk novella ''Prisoner of War'' both involve characters of a species that resemble humanoid foxes, feature characters who express similar religious and political views, and have a protagonist named Lord Rolas Darktail. But it wasn't confirmed as the same 'verse until ''Shadow of her Sins'' in the former series, which featured a minor character from Gerwart, an expy of Germany from "POW".
* There's a ''{{Flashman}}'' book where the title character (himself originally from ''Tom Brown's Schooldays'') encounters SherlockHolmes, Watson and their nemesis Tiger Moran.
* Creator/SteveAlten 's flagship ''Literature/{{Meg}}'' series and his seventh novel, ''The Loch'', became part of the same continuity with the latter book's sequel ''Vostok''.
[[/folder]]

[[folder:Live Action TV]]
* Creator/RussellTDavies:
** He has suggested that Adam Mitchell's mum in ''Series/DoctorWho'', played by Judy Holt, may be the same person as Sister Mitchell in ''ChildrensWard'', also played by Judy Holt, which would bring RTD's earlier programme into the {{Whoniverse}}. He was ''probably'' joking.
** Tthe Literature/DoctorWhoNewAdventures novel ''Damaged Goods'', which Davies wrote before being handed the series revival, has a scene near the end featuring a UNIT investigator who is implied to be the protagonist of his earlier series ''Series/DarkSeason''.
** ''Doctor Who'' has also crossed over with ''Franchise/{{Quatermass}}'', thanks to both being BBC creations and seminal British sci-fi. It started with a jokey reference to Quatermass' British Rocket Group in ''Remembrance of the Daleks'', then the tie-in books made it explicit when Quatermass turned up in one.
** The Tenth Doctor talked about [[Franchise/TheHitchhikersGuideToTheGalaxy Arthur Dent]] like he had met the guy.
--> The Doctor: Very Arthur Dent. Now, there was a nice man.
** Shortly after the ''Series/{{Torchwood}}'' base in Cardiff was blown up in the series' third season, a confused [[TeamPet pterodactyl]] was picked up by the British {{Sanctuary}}. Probably just coincidence or a shout-out, but still: the beast was never seen or mentioned again on Torchwood...
* Rumors abound to this day that Patrick [=McGoohan=]'s Number 6 from ''Series/ThePrisoner'' is the same character as John Drake, his role in the earlier series ''Series/DangerMan''. [=McGoohan=] always denied it while other people involved in the show supported it, in what was probably a deliberate attempt to screw with the fans some more.
** It's been suggested that [=McGoohan=] tended to deny it solely because he didn't hold the rights to his previous role, and thus, establishing a direct connection could be considered copyright infringement (and thus, potentially actionable). His co-writer on the series has always claimed that it was definitely Drake, though.
* Although the Showtime revival of ''Series/TheOuterLimits'' was an anthology show, it usually ended its seasons with money-saving clip shows tying multiple prior episodes together into a single continuity.
* ''PowerRangers'' has gone through this a few times. While the first six seasons were all one storyline and the seventh (''Series/PowerRangersLostGalaxy'') was a direct sequel, each one past that has been self-contained; though many would make small references to prior seasons or at least eventually team up with the prior season's cast. Only two seasons (''Series/PowerRangersNinjaStorm'' and ''Series/PowerRangersRPM'') have been welded in after the fact, having nothing in themselves to connect to the rest of the franchise; and the third unconnected season (''Series/PowerRangersJungleFury'') has been welded into ''Series/PowerRangersMegaforce'''s CrisisCrossover. Also notable was that ''Series/PowerRangersLightspeedRescue'' welding itself to ''Lost Galaxy'' retconned the latter from TwentyMinutesIntoTheFuture to the present day. Interestingly, ''Lost Galaxy'' once referenced the universal coordinates of the location of planet Gallifrey, meaning ''Doctor Who'' may also be part of the Power Rangers 'verse.
* Later ''Franchise/KamenRider'' shows have taken steps to establish that the various characters created by ShotaroIshinomori (or at least AlternateUniverse versions of them) exist in the same universe. For example, characters from ''SpaceIronmenKyodain'' appeared as the antagonists of one of the ''KamenRiderFourze'' movies, while Inazuman appeared in the crossover movie between ''Fourze'' and ''KamenRiderWizard''. ''KamenRiderGaim'' also had a crossover with ''{{Kikaider}}'' designed to promote the latter's new movie.
* The Disney Channel has done several crossovers with their live action series, so that [[Series/ThatsSoRaven psychics]], [[Series/WizardsOfWaverlyPlace wizards]], [[Series/TheSuiteLifeOfZackAndCody Tipton Industries]], [[CoryInTheHouse President Martinez]], [[ImInTheBand Iron Weasel]], and HannahMontana all exist in the same [[{{DCLAU}} universe]].
* It's been more-or-less established that all Nickelodeon sitcoms beginning with DrakeAndJosh all have some form of connection. Eventually enough crossovers happened for the NickVerse to form. It is horrendously complicated by the fact that due to the way it came about, the actors and characters all exist alongside each other as real people. It includes Series/DrakeAndJosh, Series/{{Zoey101}}, Series/ICarly, {{Victorious}} and also causes Series/BigTimeRush and Series/TheNakedBrothersBand to enter the universe, via MirandaCosgrove showing up AsHerself on both those shows. This could somewhat more accurately (and awkwardly) be referred to as the Schneider-verse, for showrunner Dan Schneider.
* In the last episode of ''SpinCity'' where MichaelJFox appears as a regular, it is suggested that the series takes place in the same universe as ''Series/FamilyTies''.
* Creator/StevenMoffat has welded a fair number of his series together over the years: ''{{Chalk}}'' contained frequent references to ''PressGang'', and was in turn referred back to by ''{{Coupling}}''; ''{{Jekyll}}'' also referred to ''PressGang'' and ''{{Coupling}}'' has references to ''JokingApart''.
* Lisa Kudrow, who played a quirky waitress on MadAboutYou, played Phoebe on ''{{Friends}}''. It was later revealed they were twin sisters and Ursula (the waitress) became a recurring character. It was also revealed that Paul once lived in the apartment now occupied by Kramer on {{Seinfeld}}.
** In the second season of ''Friends'', there was a brief crossover with ''Series/CarolineInTheCity''. Matthew Perry had a brief appearance on the Caroline episode as Chandler while Lea Thompson had an appearance Caroline in the Friends episode. Expanding beyond those two, earlier that same season [[Series/{{Frasier}} Niles Crane and Daphne Moon]] appeared in one ''Caroline'' episode, and Frasier himself showed up in an episode of ''Series/{{Wings}}.'' Based on this logic, potentially every NBC sitcom that ran during the 90's takes place in the same world (and also proceeds to directly tie into the Westphall example below)
* Taking this to the extreme, due to various character cameos and crossovers, much of television history may take place in the mind of StElsewhere's [[http://home.vicnet.net.au/~kwgow/crossovers.html Tommy Westphall]].
* Thanks to ''Franchise/LawAndOrder'' character John Munch, the Law and Order [[CashCowFranchise franchise]] managed to bring in ''Series/{{NCIS}}'', ''Series/NCISLosAngeles'', ''Series/{{JAG}}'', ''First Monday'', ''InPlainSight'', ''The Beat'', ''Series/HomicideLifeOnTheStreet'', ''Series/HawaiiFive0'', ''TheWire'', ''Series/ArrestedDevelopment'', ''Series/TheXFiles'', ''TheLoneGunmen'', and ''Series/{{Millennium}}'' all into a single universe through his constant crossover appearances. (Which also fits into the Westphall Hypothesis above.)
** The scariest part of that link? The X-Files crossed over with Cops, a reality show, meaning that all those shows take place in our universe... Which is, of course, the imagination of an autistic boy with a snowglobe.
** NBC has also announced a crossover between ''Series/ChicagoPD'' and ''Franchise/LawAndOrder'':'' [=SVU=]'', this means that ''Series/ChicagoPD'' and ''Series/ChicagoFire'' are also part of this verse.
* There was a crossover between ''Series/MurderSheWrote'' and ''Series/MagnumPI", and one between ''Series/MagnumPI'' and ''Series/SimonAndSimon''. Accordingly, all three are in the same universe.
[[/folder]]

[[folder:Mythology]]
* RobinHood went through several rounds of this, along with AdaptationDisplacement. Maid Marion, Friar Tuck, and Alan-a-Dale were all characters from separate folk tales, and it was only later that Robin Hood stories had anything to do with Richard the Lionheart or Prince John.
[[/folder]]

[[folder:Pinball]]
* ''Pinball/ThePartyZone'' takes three of Creator/DennisNordman's games -- ''Party Animal, Pinball/ElviraAndThePartyMonsters,'' and ''Pinball/DrDude'' -- and gives them in a shared continuity they never had before.
[[/folder]]

[[folder:Tabletop RPG]]
* An odd version of this exists in ''TabletopGame/DungeonsAndDragons''. Gods cross over from one campaign setting to another, spells exist under different names, and so on. Initially the settings were welded only by implication, mostly mythological crossovers (shared gods) and in the names of spells ("Bigby's Grasping hand", "Mordenkainen's Hound") indicating that divine beings and powerful wizards COULD go where they wished, but providing no actual explanation. Later, the ''{{Planescape}}'' and ''{{Spelljammer}}'' meta-settings provided two (amusingly contradictory) explanations: in Planescape a stock-fantasy multiverse exists, with the added benefit of explaining where all the more biologically impossible elemental and evolutionarily improbable critters come from. In Spelljammer the medieval cosmology turned out to be true, and adventurers can sail between the various crystal spheres in mighty magical craft riding currents in the lumnoferous aether.
** There was also the [[InnBetweenTheWorlds World Serpent Inn]], which even links campaign settings which are explicitly not part of the Planescape/Spelljammer cosmology, such as ''{{Eberron}}''.
** {{Ravenloft}} is, itself, a product of Canon Welding, as its PatchworkMap incorporates several domains that were inspired, copied, and/or outright stolen from other AD&D campaign worlds. ''Literally'' stolen, in some cases.
** The "legendary" settings of the various AD&D Historical Reference books were eventually revealed - in the appendix to ''[[TimeTravel Chronomancer]]'' - to be the past of Gothic Earth from ''{{Ravenloft}}: Masque of the Red Death''...which in turn may the past of one of the magical D20Modern settings - probably Shadow Chasers (the Red Death gets mentioned in the ''Menace Manual'').
* The ''TableTopGame/OldWorldOfDarkness'' was originally a set of unrelated {{tabletop RPG}}s which shared the same basic gameplay. Then White Wolf decided to link them all together, with rather strange results. While werewolves could reasonably fit into the same setting as vampires or mages, trying to jam vampires and mages into the same setting was a trick endeavour, given that both groups were said to have been secretly manipulating human history since the dawn of time (also because "being alive" is the primary protection against a mage lighting something on fire with his mind and mages can identify other supernaturals and tag them as dangerous instantly, so vampires tended to last about a minute tops in those crossovers). The new version is made with the possibility of such crossovers explicitly in mind, at the same time keeping each group at arm's length - the storyteller is not required to have them all exist if she or he doesn't want to, but the crossover rules ensure there'll be few to no snarls if they do. For example, the Supernal Realms of ''TabletopGame/MageTheAwakening'' and the Shadow World of ''WerewolfTheForsaken'' have little to do with each other, but equally don't step on each other's cosmological toes.
** The Shadow World is also explicitly part of the Mage cosmology. The only problem we currently have with the cosmology is the "Two Arcadias" hypothesis. In Mage, {{Arcadia}} is the [[AscendToAHigherPlaneOfExistence Supernal]] Realm of Time and Fate, and separated from the human world by the [[EldritchAbomination Abyss]], a massive rent in reality; while in ''TabletopGame/ChangelingTheLost'', Arcadia is a realm where humans are kidnapped off to and transformed into Changelings. Some believe that these are two different realms, while others believe they are the same realm. The books state that the answer is to be determined by the GameMaster, but offers suggestions for both options. It's also possible that [[TakeAThirdOption both are true]]: there is a "Fallen" Arcadia and a "Supernal" Arcadia which were originally one realm and are now separated by the Abyss, but the Watchtower of the Lunargent Thorn bridges the gap and allows them to intersect and interact.
** Actually, in both iterations of Mage no one actually knowing the origin of Mage civilization and the ultimate destiny of the ascended is both a plot point and a core theme. All of these things are not only possible, but a storyteller is actively encouraged to change which is implied to be true from moment to moment, sometimes imply that some, all, or none are true at once, etc more or less at random. It's intentional that the players, like the magi, should always feel that there's information that's absolutely vital that lies just beyond their grasp: finding out for sure is called 'ascending', and either you can't come back or no one's bothered yet.
** ''{{Exalted}}'' was an inversion. The original concept for the game was for it to be set in the forgotten, mythical prehistory of the ''Old World of Darkness''... but it was ultimately decided not to make this an absolute of the setting, and reduce the connections to common setting elements and parallels that hint at the possibility. The tagline "Before there was a world of darkness..." is TheArtifact of the original concept.
* ''{{Rifts}}''. Want ''Robotech'' mecha to fight the Teenage Mutant Ninja Turtles alongside unicorn-riding cyborgs, only to have them all ambushed by eldritch abominations? Rifts. Palladium games specifically published conversion books for incorporating their other franchises into Rifts rules.
** Which is mostly a case of converting some things to MDC. Other than that, every Palladium game uses the same basic rules. Another bit of Canon Welding comes in-universe. Hints have been dropped in the books that Rifts Earth is either a future version of ''Beyond the Supernatural'', ''Heroes Unlimited'', or a bizarre combination of the two.
* The ''TabletopGame/{{Warhammer}}'' and ''TabletopGame/{{Warhammer 40000}}'' universes used to be linked, although the linking statements were made by mad characters. The whole saga/background is told through an UnreliableNarrator anyway. [[WordOfGod Games Workshop]] has stated that the link is now done away with, since it was mostly silly anyway. Warhammer world used to be a planet in the 40k universe, surrounded by warp storms that made it inaccessible for the rest of the galaxy. Nowdays they exist in separate universes, but there appears to be a small link between them in the form of the Warp (the Chaos Gods are the same in each universe, and some people in Warhammer world have gotten visions of Chaos in 40 universe. For example, in ''Liber Chaotica: Book of Khorne'', it's all but outright stated the author is having visions of Abaddon's 13th Black Crusade. Also the [[{{Precursors}} Old Ones]] in ''Warhammer'' appear to be the same as the ones in 40k, and a fan theory suggests they escaped from 40k universe to ''Warhammer'' one after the War in Heaven). There is no real interaction between the two universes, however, unless you count some daemon characters popping up in both universes and a few magic items that have a suspicious resemblance to 40k technology.
** It also used to be fairly heavily implied that Sigmar (the fantasy Empire's messiah figure and founder) was one of the missing Primarchs (genetically enhanced superhuman offspring of 40k's Emperor).
** Warhammer 40 000 is now considered to be simply the SpiritualSuccessor where everything is an {{expy}} of the original Warhammer Fantasy.
* The ''TabletopGame/{{GURPS}}'' Infinite Worlds setting ties together every alternate universe they ever came up with and every licensed work ever adapted to ''GURPS'' from ''Literature/{{Uplift}}'' to ''Literature/{{Discworld}}'' to ''ComicBook/{{Hellboy}}''.
* ''{{Earthdawn}}'' is canonically set in the distant past of the ''{{Shadowrun}}'' setting.
[[/folder]]

[[folder:Theme Parks]]
* In ''Ride/JimmyNeutronsNicktoonBlast'', all of the Nicktoons are shown as existing together in a large multiverse, with the soundstages acting as portals between their worlds.
[[/folder]]

[[folder:Radio]]
* Franchise/TheGreenHornet was the son of TheLoneRanger's nephew back when the two were on the radio. However due to legal issues between those who currently own the two franchises, the connection isn't used at all anymore.
* When ''TheLastChanceDetectives'' were adapted to radio, their premiere episode included an appearance by Jason Whittaker of ''AdventuresInOdyssey'', welding the two previously unrelated Focus on the Family franchises.
[[/folder]]

[[folder:Video Games]]
* ''VideoGame/StreetFighterAlpha'' effectively combined the ''Franchise/StreetFighter'' and ''VideoGame/FinalFight'' franchises into one shared {{continuity}}, by featuring Guy and Sodom from the first ''VideoGame/FinalFight'' as playable characters, followed by Rolento in ''Alpha 2'' and Cody in ''Alpha 3''..
** On the other hand, ''VideoGame/FinalFight'' was originally intended to be a {{sequel}} to the [[VideoGame/StreetFighter first]] ''Street Fighter'', and most importantly the two franchises had been already officially part of the same {{continuity}} since the console version of ''VideoGame/StreetFighterII'' first came out (proof of this was in the [[AllThereInTheManual instruction booklet]]).
* ''VideoGame/MegaManLegends'' was originally in its own {{continuity}} (hence jokes and references to the original series being a ShowWithinAShow). However, ''VideoGame/MegaManZero'' and ''VideoGame/MegaManZX'' [[VideoGame games]] have more directly connected it as being the far distant future of the original ''VideoGame/MegaManClassic'' and ''VideoGame/MegaManX''.
* When SNK made ''Art of Fighting 2'', they decided to officially make the ''VideoGame/ArtOfFighting'' series part of the same {{continuity}} as the ''VideoGame/FatalFury'' series. To explain why the ''Art of Fighting'' cast were not around during the events of the ''Fatal Fury'' games, they made the ''Art of Fighting'' series a {{prequel}} to the ''Fatal Fury'' series by setting it ten years before and putting a young Geese Howard as the TrueFinalBoss in ''Art of Fighting 2'' (back when he was still the police commissioner of South Town). When SNK later wanted to cross the ''Fatal Fury'' cast with the ''Art of Fighting'' cast in ''VideoGame/TheKingOfFighters'' games, they had to place the third series in a separate {{continuity}}.
** And from there, it starts getting ''really'' weird, with Ralf and Clark from ''VideoGame/IkariWarriors'' and Athena from ''VideoGame/PsychoSoldier'' (who is the descendant/ambiguously-the-reincarnation of the Athena from ''VideoGame/{{Athena}}'') appearing in ''VideoGame/TheKingOfFighters'' -- despite ''Psycho Soldier'' involving an invasion of monsters from beneath the Earth that you'd kind of think would get mentioned at some point in ''KOF'' canon if it happened -- and then both Ralf and Clark and ''KOF'' original Leona appearing in ''VideoGame/MetalSlug 6'' and ''Metal Slug 7''. At this point, the only sane response to the Creator/{{SNK}} canon is to throw up your hands and shout "I don't know!"
** And that's ''[[ContinuityCreep still]]'' not the half of it. Other SNK titles, from ''VideoGame/SamuraiShodown'' to ''VideoGame/TheLastBlade'' to ''[[VideoGame/FuunSeries Savage Reign/Kizuna Encounter]]'', have been alluded to in varying extents throughout ''KOF''[='s=] run.
* The ''Franchise/FinalFantasy'' series has a few counts of direct crossover, such as [[VideoGame/FinalFantasyV Gilgamesh]] (seems to be the same person in every game he appears in, which was finally confirmed in ''[[VideoGame/DissidiaFinalFantasy Dissidia 012]]'') and [[VideoGame/FinalFantasyVII Cloud]] (who features as a guest character in ''VideoGame/FinalFantasyTactics'') The remastered version of for Tactics for PSP, also adds [[FinalFantasyXII Balthier]] and [[FinalFantasyTacticsA2 Luso]]
** Ivalice Alliance series was the first attempt to make a ''Final Fantasy'' universe that included more than one game and in fact includes games without the ''Final Fantasy'' name. ''Final Fantasy Tactics'', the ''VideoGame/FinalFantasyXII'' titles, ''VideoGame/VagrantStory'', ''VideoGame/CrystalDefenders'', and the [[{{Vaporware}} not yet released]] ''Fortress'' are among the comfirmed games to take place in the Ivalice universe.
** Hints have been dropped [[VideoGame/FinalFantasyX2 here and there]] (and WordOfGod has outright stated) that ''VideoGame/FinalFantasyVII'' takes place in the far future of the ''VideoGame/FinalFantasyX'' world, on a different planet.
** And then ''VideoGame/DissidiaFinalFantasy'' made it so they're all parallel worlds in a shared multiverse, although its canonicity is uncertain. Would make sense, though. It is a series.
** ''[[VideoGame/FinalFantasyIVTheAfterYears Final Fantasy IV: The After Years]]'' reveals that every crystal-based ''Final Fantasy'' game is in the same universe. [[spoiler:The crystals are placed on a planet with promise, both to guide and record the evolution of the planets; hence why they all have humans, and not-entirely-different environments from the other ''Final Fantasies''. To prove it, the party fights such recorded monsters as [[VideoGame/FinalFantasyI The Four Fiends]], [[VideoGame/FinalFantasyIII the Dark World Crystal Guardians]], [[VideoGame/FinalFantasyV Gilgamesh, and the superbosses Omega, Shinryu]], [[VideoGame/FinalFantasyVI Death Gaze and Ultima Weapon]].]]
* When the Czech developers of ''OperationFlashpoint: Cold War Crisis'' (their first game) Bohemia Interactive Studios split with the publisher, they were able to keep the "assets" (i.e. the game engine) but not the name, so they ended up creating a SpiritualSuccessor called ''ARMA''. However, BIS has since come out and said that both series are in a SharedUniverse, as will be BIS' spin-off ''Videogame/TakeOnHelicopters''.
** The latest patch for Operation Flashpoint even renames it to ''ARMA: Cold War Assault''. Talk about paying attention to details.
* ''VideoGame/SuperSmashBros'' takes place in a universe in which the characters of every single Creator/{{Nintendo}} series from ''Franchise/SuperMarioBros'' to ''Franchise/TheLegendOfZelda'' to ''VideoGame/{{Kirby}}'' as well as ''Franchise/SonicTheHedgehog'' and ''Franchise/MetalGear'' co-exist in the same verse. However, it's obvious that the series takes place in an AlternateContinuity as the canon backstory of the series is that Master Hand brought to life Nintendo characters from the form of dolls (that would later be replaced with trophies from ''Melee'' onward) in order to have them fight one another.
* The [[MegaCorp Ultor Corporation]], from ''RedFaction'', a science-fiction series about Martian rebels, makes an appearance in ''SaintsRow'', a series about gang warfare in a contemporary American city. ''RedFaction: Guerilla'' references this with "Mount Vogel", named after the CEO of Ultor in ''SaintsRow2''.
** This started off as a ShoutOut in the original ''SaintsRow'', with a few references to Ultor here and there. Then ''SaintsRow2'' ran with it, and made Ultor a major faction that is clearly the same one as in ''RedFaction''.
* The sheer amount of shout-outs to ''[[VideoGame/NightsIntoDreams NiGHTS]]'' in the ''Franchise/SonicTheHedgehog'' series has led some people (including those of semi-official status) to claim they are in the same universe.
* ElementalWarOfMagic shares a ''lot'' of its terminology (especially in its backstory) with GalacticCivilizations, indicating that the game may be set on ancient Altaria and the channellers are SufficientlyAdvancedAliens.
* ''VideoGame/BetrayalAtKrondor'' and ''[[TheRiftwarCycle Riftwar]]''.
* {{Easter egg}}s in {{Sierra}}'s adventure games point to a shared continuity.
* Creator/NamcoBandai seems to have merged parts of the previously unrelated (despite numerous {{Shout Out}}s) ''VideoGame/{{Galaxian}}''[=/=]''VideoGame/{{Galaga}}'' series, ''VideoGame/AceCombat'' series, ''VideoGame/RidgeRacer'' series, and some other games into an overarching ''[[http://acecombat.wikia.com/wiki/United_Galaxy_Space_Force United Galaxy Space Force]]'' series.
* In the PC game series ''VideoGame/DarkParables'', [[AllMythsAreTrue all fairy tales are true]], and they're all pretty much part of one gigantic story. Literature/SleepingBeauty is sister-in-law to Literature/TheFrogPrince and [[Literature/TheSnowQueen Gerda]] is descended from [[Literature/HanselAndGretel Hansel]], for starters.
* ''VideoGame/CommanderKeen'' and ''VideoGame/Wolfenstein3D'' are linked together by way of Commander Keen's Billy Blaze being the grandson of Wolfenstein's B.J. Blazkowicz. A common fan theory is that the protagonist of ''VideoGame/{{Doom}}'' is also part of the family. The RPG versions of their respective games go with this - the "Harbinger of Doom" from ''Wolfenstein RPG'' is basically ''Doom'''s Cyberdemon without prosthetics, and the hero of ''Doom RPG'' is explicitly given the last name "Blazkowicz".
* Ever since 2004 ''VideoGame/NinjaGaiden'' has been established to be in canon with ''Franchise/DeadOrAlive'' series with Ryu being the canonical winner of the second tournament and ''Dead or Alive'' character [[ActionGirl Ayane]] acting as a support character throughout many ''Ninja Gaiden'' installments.
* Up until ''VideoGame/FireEmblemAwakening'', it was assumed that barring remakes and direct sequels/prequels, all ''Franchise/FireEmblem'' games were set in different universes and did not impact each other. However, [=SpotPass=] and DLC content for ''Awakening'' used characters from previous ''Fire Emblem'' games--including ones that were not set in the [[VideoGame/FireEmblemAkaneia Archanea universe]]--and so to get around this, introduced a "gateway" (the Outrealm Gate) that allowed characters to travel between the different universes. This would imply that all of the worlds are connected, physically or otherwise, as part of some greater universe rather than separate, alternate worlds.
* Could very well be happening to ''VideoGame/AssassinsCreed'' and ''VideoGame/FarCry'', if Far Cry 3's DLC is anything to go by.
* Discussed in ''VideoGame/ProjectXZone'' where (on top of canonizing about a dozen other crossover games) the characters from the many different universes have some fun trying to link them together. For instance, the characters of ''VideoGame/GodsEaterBurst'' find it plausible that their world would continue on a downward spiral, necessitating the construction of [[VideoGame/ResonanceOfFate Basel]] in their far future. However, it's also acknowledged that certain universes are mutually exclusive with each other (''VideoGame/SakuraWars'' is technologically and geopolitically incompatible with modern earth) or completely isolated (''VideoGame/TalesOfVesperia'' is shown to be in its own disconnected bubble), so nothing is set in stone.
* ''VideoGame/QuakeIIIArena'' mashes ''VideoGame/{{Doom}}, VideoGame/{{Quake}}'', and ''VideoGame/QuakeII'' into a single continuity.
* The [=PS2=]-era ''VideoGame/GrandTheftAuto'' games are in the same continuity as the ''VideoGame/{{Manhunt}}'' series - Carcer City is explicitly stated to be a location in the Grand Theft Autoverse, and it was introduced even before Manhunt was released. And the ''{{Grand Theft Auto IV}}'' universe (which it shares with ''GrandTheftAutoV'') may be shared with ''VideoGame/{{Bully}}'', with the appearance of the Bullworth Academy on TV.
* [[CapcomVsWhatever Some of Capcom's more robust crossovers]], like ''VideoGame/TatsunokoVsCapcom'' and ''VideoGame/MarvelVsCapcom3'', imply that many a Capcom franchise share some implicit but mostly unexplored degree of connectivity (going beyond the SharedUniverse the ''Franchise/StreetFighter'' franchise is known to be part of). For example, [[VideoGame/{{Darkstalkers}} Morrigan]] in ''[=TvC=]'' expresses disappointment that VideoGame/ViewtifulJoe didn't live up to what she learned from Joe's rival Alastor. Alastor, as per the [=PS2=] version of ''Viewtiful Joe'', is the spirit of the sword Dante picks up in the original ''VideoGame/DevilMayCry'' and Dante's (admittedly non-canon) story in ''Viewtiful Joe'' [[spoiler:has Mundus, the BigBad of ''[=DMC1=]'', as TheManBehindTheMan]]. Likewise, Dante and Joe are shown to be buddies/friendly rivals in their ''[=MvC3=]'' intro quotes for each other, which would be strange (seeing as they never actually met in ''Viewtiful Joe'') if not for the fact that Dante was a playable character in the PSP port of ''Viewtiful Joe: Red Hot Rumble''.
** If that wasn't enough, there are multiple hints throughout ''VideoGame/{{Bayonetta}}'' pointing to the fact that [[IntercontinuityCrossover it exists in the same world as]] ''Devil May Cry''. Given that ''DMC'' and ''Bayonetta'' were [[Creator/HidekiKamiya created by the same guy]] (who was also responsible for the first ''Viewtiful Joe''), this is not entirely surprising.
* Way back in the Amiga days, ''Super VideoGame/{{Turrican}}'' took place on the planet of VideoGame/{{Katakis}}. This was referenced in the Turrican clone ''Hurrican'', which took place on the planet Takatis (which was the name of a clone of Katakis by the same team, [=Poke53280=]).
[[/folder]]

[[folder:Webcomics]]
* The ''Webcomic/MSPaintAdventures'' series ''Webcomic/ProblemSleuth'' was tied into the earlier ''Webcomic/{{Jailbreak}}'' series when Zombie Ace Dick and his whale crashed into the jail where ''Jailbreak'' was set. Indeed, a dead whale was part of an early ''Jailbreak'' puzzle, and ZAD and the Completely Sane Man were revealed to be the skeletons in one of the cells.
** In another example, ''Webcomic/{{Homestuck}}'''s [[ShowWithinAShow Comic Within A Comic]] ''{SweetBroAndHellaJeff'' predates ''Homestuck''. It was originally written as a parody of another {{webcomic}} called ''[[http://forums.penny-arcade.com/showthread.php?t=85435&page=3 Higher Technology]]'', and was written into ''Homestuck'' as a {{webcomic}} run by Dave Strider.
** In a semi-canonical donation extra the ''ProblemSleuth'' characters did battle with the Midnight Crew. That gang would later become extremely plot important in ''{{Homestuck}}''. Even though both Problem Sleuth ''and'' the Midnight Crew exist as fictional works in the Homestuck universe - in fact, instead of Homestuck, in-universe the [[MsPaintAdventures adventure]] following Problem Sleuth was based on The Midnight Crew. To confuse the issue further, an Easter Egg in Homestuck implies that Problem Sleuth took place on Prospit, making Problem Sleuth canon to the Homestuck multiverse.
* In ''StarslipCrisis'', the character of Vore is all but explicitly stated to be in fact Vaporware from the author's previous comic, ''CheckerboardNightmare''. However, this can be considered only to be a partial example, since said strip's events are never mentioned in ''[[StarslipCrisis Starslip]]'' and Vore himself seems to have lost his memory up to that point, causing a bit of a personality change (yes, Vaporware also expressed desires to exterminate mankind, but Vore's a lot more proactive about it), so for all intents and purposes Vore can be considered a separate character. Eventually he did regain his old memories and personality, and started calling himself Vaporware again...[[spoiler:right before he was killed off for real.]]
** On the other hand, records of the past (or Real Life, 21st Century Earth) seem to be extremely sketchy, as evidenced by the ShowWithinAShow "Concrete Universe," where covered wagons exist at the same time as cloning.
* ''CrossoverWars'' and ''Webcomic/TheCrossoverlord'' established many {{webcomic}}s as part of the same {{multiverse}} with rules more akin to Westphall's mind. The [[http://www.webcomicsnation.com/crossoverlord/REALITEASE.php Realitease]] [[AllThereInTheManual page]] done by ''[[Webcomic/TheCrossoverlord Crossoverlord]]'' creators contains interesting informations about which {{webcomic}}s happens in the same universe with lists of proofs and explanations:
** ''WebComic/{{Fans}}'' and ''Webcomic/CollegeRoomiesFromHell'' seems to be set not only in the same universe but also share it with ''eight'' other {{webcomic}}s.
** ''Webcomic/SomethingPositive'' shares a world with ''Webcomic/QueenOfWands'', ''Webcomic/PunchAnPie'', ''Scandal Sheet'', ''Webcomic/GirlsWithSlingshots'', ''Webcomic/QuestionableContent'', ''Webcomic/{{Shortpacked}}'', ''Webcomic/PennyAndAggie'' and ''All New Issues''. For example, the cats from [=S*P=] and GWS had a litter of hypoallergenic kittens.
** ''Webcomic/MegaTokyo'', ''AppleGeeks'', ''CtrlAltDel'', ''QuestionableContent'', ''[[WalkyVerse Shortpacked]]'' and ''DieselSweeties'' are all set in one universe. Also, one of the hypoallergenic kittens of [[SomethingPositive Choo-Choo Bear]] and [[GirlsWithSlingshots Sprinkles]] ("the fat one") was given to [[{{Walkyverse}} Leslie Bean]] by her lesbian lover's sister, Roz in a weird, drug deal-like handoff with [[SomethingPositive Davan]]. In the words of [[{{Walkyverse}} David Willis]], "{{Webcomics}} are so incestuous".
** ''{{Mindmistress}}'' shares a universe with ''ClanOfTheCats'' and ''LCD'', as well as with ''ZebraGirl'' or her alternate counterpart.
** Webcomic/{{Crossoverkill}} fueled the fire, not only adding more webcomics to TheMultiverse, but also with revelation that Doppleganger Gang members are all alternate reality counterparts of one another and there are members from viarous webcomics among them, including several fantasy webcomics.
* ''HeroesUnite'' did it with a horrifying amount of SuperHero {{webcomic}}s, hosted on DrunkDuck. First it estabilished that ''{{Energize}}'', ''Bombshell,'' and an alternate counterpart of {{Acrobat}} share an universe, and then a bunch of other superheroes joined in. Some writers even took an advantage of it to make their webcomics more popular. The creators of ''{{Energize}}'' and ''Webcomic/{{Dasien}}'' did a short (currently on hiauts) crossover between their characters, while the former used a new SharedUniverse to bring back his other {{webcomic}}s - ''Fearless'', {{SHELL}} teamed up with TheBlondeMarvel and Bombshell and gets his ass kicked by one of HeroForce members before joining HU, and Vora, Princess Of The Skies, appeared a few times in HU before getting her own adventures. And it's all one reality in the {{webcomic}}s {{multiverse}}.
** Having kickstarted the whole superhero crossover thing on DrunkDuck, HeroesUnite is now set in its own self-contained universe, but the crossover goodness continues in the spinoff HeroesAlliance with the characters from KarabearComicsUnlimited and even involved JennyEverywhere and golden age characters like Madame Fatal.
* T Campbell has done this with various webcomics he's written or co-authored, both played straight and using alternate versions of characters.
** ''PennyAndAggie'', ''Cool Cat Studio'' and ''Sketchies'' are set in the same universe. However, the SF and supernatural elements in ''Cool Cat Studio'' are absent from the other two comics. Campbell once [[WordOfGod explained]] this on the ''P&A'' forum by stating that such elements exist on the periphery of the comics' shared universe, so not all its inhabitants experience, nor are even aware of, such things. This is in contrast to the ''{{Fans}}'' universe (and its alternate versions of ''P&A'''s characters), where, particularly after the {{Revival}}, paranormal occurrences are so frequent and prominent that the entire world is aware of them.
** Also alternate versions of characters from ''PennyAndAggie'' and ''{{Fans}}'' appear in each other's universes every so often.
* Barry T. Smith's ''InkTank'' appeared to be in an entirely new universe from the previous strips...until a story arc which ended with the AuthorAvatar having a nervous breakdown was resolved by Dante from ''Angst Technology'' turning up and treating him to a coffee.
* Artist Ursula Vernon's ''Webcomic/{{Digger}}'', an anthro adventure about a mildly cynical wombat and a statue of the god Ganesh, has this if you start reading her other work. An awful lot of everything she's done seems to have characters in common with the Gearworld, her vaguely-steampunk clockwork-labyrinth art-and-fiction setting. It's only vaguely hinted at in ''Digger'' itself.
* ''SugarBits'' might have done it when one of the villains summoned Red [[spoiler: and Big Bad Wolf]] from ''Webcomic/EverAfter'' to fight protagonists. However, given the nature of the ''SugarBits'' world and [[WordOfGod Bleedman's own words]], those two comics may or may not share an universe and this will remain unresolved until Endling, creator of ''Ever After'', will confirm it.
* Shaenon Garrity's ''{{Narbonic}}'' and ''SkinHorse'' were officially confirmed to take place in the same continuity with the introduction of [[spoiler:Artie Narbon]] to Tip Wilkin. Garrity had previously revealed in ''{{Narbonic}} Director's Cut'' that the main ''Narbonic'' characters, Dave, Helen, and Mell, came from three different comics she had drawn in high school and college. Mell also gets her own SpinoffBabies comic, ''Li'l Mell'', and a character introduced in that comic has now shown up in ''SkinHorse''. Garrity's lesser-known ''{{Smithson}}'' may fit into the same continuity as well; minor character Queensbury Joe appears to be the older version of Homeschool Joe from ''Li'l Mell''.
** Mel has also appeared twice in ''EverydayHeroes'' - once in a brief flashback where Mr. Mighty thwarts one of Helen's capers and again where she appears as Dr. Unpleasant's lawyer.
* Eli Parker created several different web projects, including ''Too Far'' (a comedy space opera webcomic), ''Darthwiki/PowerupComics'' (a StealthParody of TwoGamersOnACouch webcomics), and ''Website/TheseWebComicsAreSoBad'' (another StealthParody, this time of webcomic review blogs). Then Parker created ''UnwindersTallComics'', which included cameos from all of the above, establishing that they (or at least their fictitious authors) all exist in some sort of continuity.
* There was earlier hints about ''Webcomic/BobAndGeorge'' and its fancomics/subcomics taking place in the same multiverse. Ridiculous amount of cameos got finally an explanation, when Rick O'Shay and Chick-Bot appeared in the main comic to tell the [[VoidBetweenTheWorlds true nature]] of White Space. It was a demi-plane that connected all the universes together. It was later abused by [[spoiler:[[GondorCallsForAid sending all the Mega Mans and other characters into one universe, to fight Bob]]]].
* ''Webcomic/{{Glorianna}}'' and Sparky of ''Webcomic/LadySpectraAndSparky'' shared an adventure when Glorianna was briefly transported to the 21st century (while Lady Spectra ended up in Glorianna's era).
[[/folder]]

[[folder:Web Original]]
* The (In)Famous Creator/DavidGonterman, Creator/EdWood of the World Wide Web and the Internet's Most Dangerous Cartoonist; reuses characters, concepts and names so often that it more or less seems that every single thing he's ever written or drawn are all set in the same vague universe/{{multiverse}}. This may be partially intentional, but, well...
* Website/ThatGuyWithTheGlasses likes this {{trope}}, finally creating an official merging of every TGWTG-involved character during the huge anniversary brawl, and again during ''WebVideo/{{Kickassia}}'', ''WebVideo/SuburbanKnights'' and ''WebVideo/ToBoldlyFlee'', not to mention the millions of crossovers between producers.
* Franchise/TheFearMythos incorporates Franchise/TheSlenderManMythos into their canon as well as The Black Dog from folklores of the British Isles and later incorporated the Smiling Man from Blog/TheJeanetteExperience as a Canon Immigrant.
** The CthulhuMythos is a part of it too, with the blog [[http://mephirevolution.blogspot.com/ Mephi]], having many of Lovecraft's creatures being a major part of the story.
* [[WMG/FriendsAndTheHighCouncil The Friends and the High Council WMG]] is an attempt to do this [[UpToEleven with every Disney-owned property]].
[[/folder]]

[[folder:Western Animation]]
* Creator/{{Disney}}, if you can believe it, did this. ''WesternAnimation/LiloAndStitchTheSeries'' had {{Crossover}}s with ''WesternAnimation/KimPossible'', ''WesternAnimation/TheProudFamily'', ''WesternAnimation/{{Recess}}'', and ''WesternAnimation/AmericanDragonJakeLong''.
** Ingrid Third was also clearly visible in the background in ''WesternAnimation/AmericanDragonJakeLong'', adding ''WesternAnimation/{{Fillmore}}'' to the list.
** There was also an episode of ''Disney/{{Hercules}}'' in which Jafar and Hades cut a deal to eliminate each other's enemies, resulting in an ''Disney/{{Aladdin}}'' {{Crossover}}.
** While ''WesternAnimation/DuckTales'' and ''WesternAnimation/DarkwingDuck'' were obviously part of the same universe what with both shows having Launchpad [=McQuack=], a ''DisneyAdventures'' story known as ''ComicBook/TheLegendOfTheChaosGod'' establishes ''WesternAnimation/GoofTroop'', ''WesternAnimation/TaleSpin'', and ''WesternAnimation/ChipNDaleRescueRangers'' are part of the same universe as well.
** ''WesternAnimation/{{Gargoyles}}'' WordOfGod, GregWeisman, says it shares its universe with ''Disney/AtlantisTheLostEmpire''—or at least, each 'verse includes a BroadStrokes version of the other franchise. (This occurred when Weisman worked on an ''Atlantis'' TV {{spinoff}}—but the series, including the ''Gargoyles'' CrossThrough episode, got canned when the movie bombed.)
** The ''VideoGame/KingdomHearts'' series of video games has most major Disney worlds, or rather, explicitly AU versions of them, existing in a larger multiverse.
* In the ''WesternAnimation/SouthPark'' episode "Super Best Friends", there is a brief scene of the cast of ''ThatsMyBush'' in the White House, indicating that the two series (both created by Matt Stone and Trey Parker) take place in the same universe (which is particularly silly, since ''ThatsMyBush'' is a live-action show).
** And another ComedyCentral show, ''WesternAnimation/DrKatzProfessionalTherapist.''
* There were reportedly plans to weld the canons of ''WesternAnimation/ExoSquad'' and ''Anime/{{Robotech}}'' back when the former was produced. Considering that their primary motivation seemed to be that both shows were MerchandiseDriven, your mileage may vary on whether it's a good or bad thing that this never happened. It went beyond just planning; there were figures of Robotech mecha sold in WesternAnimation/ExoSquad-branded packaging.
* ''WesternAnimation/AmericanDad''s Stan and Bullock try to stop ''WesternAnimation/FamilyGuy'''s Stewie plan to take over the world, with Stewie mistaking [[LampshadeHanging Stan for Joe]]. [[spoiler:Of course, this takes place in a virtual reality simulation, so it's debatable weather it's canon or not.]] There have been a few other smaller cameos.
** There is a deliberate lack of crossovers between ''Family Guy'' and ''American Dad'' but they're considered to be part of the same universe. However at the end of the American Dad episode "Hurricane!", [[spoiler:the houses of Cleveland and Peter end up on the both sides of Stan's house resulting in them going into a stand-off that ends with Francine accidentally being shot by Stan]]. [[StatusQuoIsGod It's never addressed in later episodes of any of the shows]].
* ''WesternAnimation/{{ThunderCats|2011}}'' (2011), as of the episode "Legacy" features new versions of characters from ''WesternAnimation/SilverHawks'' and ''[[WesternAnimation/TheComicStrip TigerSharks]]'', all of which were action shows produced by RankinBass in the '80s, sharing the same art style, writers, and voice actors. While the shows were incredibly similar and could easily be mistaken for being part of the same universe, it's only official now after twenty plus years.
* ''TheVentureBros'' attempted to weld itself onto the ''JonnyQuest'' canon, even going as far as to feature Race Bannon as a character in one episode, but after Hanna-Barbera protested it, all references to Jonny Quest were quietly replaced with LawyerFriendlyCameo versions.
* RankinBassProductions is also famous for its adaptations of Christmas stories, and eventually welded many of them together in a movie called ''Rudolph and Frosty's Christmas in July.'' Naturally there were a lot of elements that did not quite fit together--SantaClaus, for example, had a subtly different appearance and personality in each previous special--so decisions and adjustments were made. Likewise some scenes from Rudolph and Frosty's lives were shown that differed from their own specials, but [[BroadStrokes kept the basic facts the same]].
* Originally ''WesternAnimation/StaticShock'' referenced {{Superman}} as a fictional character but this was [[{{Retcon}} retconned]] allowing the show to be welded into the ''DCAnimatedUniverse''.
* ''WesternAnimation/TheCritic'' Jay Sherman once showed up to judge the ''WesternAnimation/TheSimpsons'' Springfield Film Festival, though Matt Groening was so against the idea that he took his name off the opening credits for that episode.
* ''WesternAnimation/TheTransformers'' have already been listed, but deserve special mention here; in the '80s, it was broadly hinted that the original cartoon shared a universe with the ''GIJoe'' cartoon, and not-quite-as-broadly that the same was true for ''WesternAnimation/{{Jem}}'' and ''WesternAnimation/{{Inhumanoids}}''[[note]]''[[WesternAnimation/MyLittlePonyAndFriends My Little Pony]]'' was close to being the same universe with a couple scenes scrapped from ''WesternAnimation/MyLittlePonyTheMovie''.[[/note]]. This has been taken much further in the 21st century, where not only were the previous hints confirmed, but now ''every'' Hasbro cartoon from the time period has been stated to be part of the same universe, and pretty much every other Hasbro property exists within the Transformers multiverse.
* The original ''WesternAnimation/SpaceGhost'' cartoon, via crossovers dealing with TimeTravel in the last six original episodes, became part of the same universe of ''WesternAnimation/DinoBoy'', ''WesternAnimation/TheHerculoids'', ''WesternAnimation/{{Shazzan}}'', ''MightyMightor'', and ''MobyDick'' (the HannaBarbera cartoon, obviously not [[Literature/MobyDick the book]]).
** Meanwhile Space Ghost has become a recurring character in the Creator/AdultSwim Universe currently consists of ''WesternAnimation/SpaceGhostCoastToCoast'', ''WesternAnimation/AquaTeenHungerForce'', ''WesternAnimation/TheBrakShow'', ''WesternAnimation/PerfectHairForever'', ''WesternAnimation/HarveyBirdmanAttorneyAtLaw'', ''WesternAnimation/TwelveOunceMouse'', and possibly ''WesternAnimation/{{Sealab 2021}}''.
** Yet another version of Space Ghost had a cameo in ''WesternAnimation/ThePowerpuffGirls'' along with Harvey Birdman. Seeing as how the Powerpuff Girls may be part of ''WesternAnimation/TheGrimAdventuresOfBillyAndMandy'' universe as mentioned above we'll just stop here.
** Space Ghost was even featured in a opening segment of a ''WesternAnimation/BatmanTheBraveAndTheBold'' episode.
* WordOfGod places ''WesternAnimation/TheAvengersEarthsMightiestHeroes'', ''WesternAnimation/WolverineAndTheXMen'', ''HulkVS'', and ''WesternAnimation/ThorTalesOfAsgard'' in the same universe. We have [[spoiler:Wolverine appearing as a member of both the Howling Commandos and New Avengers and the Mutant Response Division imprisoning Whirlwind]], as well as one ''Wolverine'' episode being a direct sequel to HulkVs. (However, contradictions do exist, mainly in the portrayal of the Hulk and which eye Fury's eyepatch is on.)
** WordOfGod has also said that the X-Men would have shown up in season three [[WhatMightHaveBeen had it not been cancelled.]]
** The show's [[AllThereInTheManual tie-in comic]] (which was written by the show's creators) blatantly contradicted this, showing versions of ScarletWitch and {{Quicksilver}} that were nothing at all like their ''WATXM'' counterparts.
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-->'''[[WebVideo/TheSpoonyExperiment Doctor Insano:]] '''[[WebVideo/AtopTheFourthWall It's Hypertime; just accept it]].
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