!!General Trivia
* Arkham is loosely based on infamous witch-town Salem, Massachusetts, while Miskatonic University is based on Gordon College (Wenham, Massachusetts) and Arkham Sanitarium (no relation to [[{{Franchise/Batman}} Arkham Asylum]]) is based on Danvers State Hospital in Danvers, Massachusetts. Curiously enough, this means LovecraftCountry is also home to Haverhill, Massachusetts -- one of the inspirations for Archie Comics' Riverdale!

!!General Tropes
* BasedOnADream: The Nightgaunts were from a nightmare Lovecraft once had, so it's rather fitting they be living in the Dreamlands.
* {{Defictionalization}}: The Necronomicon listed in the Ohio University Library card catalog. Creator/LSpragueDeCamp, fantasy author and linguist, acted as Abdul Alhazred's "translator".
* NamesTheSame: Not only are there both Great Old Ones and Old Ones and Elder Things and Elder Gods and Old Gods, there are mentions of various "old ones" and "elder ones," "ancient ones," and "old things" unconnected to the "codified" entities of those names. In addition, the influence of the Mythos will lead many sci-fi and fantasy authors to use these names for entities in their own universe, with varying degrees of similarity to the originals.
* RunningTheAsylum: An appropriate and positive example - Lovecraft encouraged his fans to use his mythology, and expanded off the concepts within those fics. Indeed, without Lovecraft's fan friends, his work would have drifted into obscurity.
* TheWikiRule: [[http://lovecraft.wikia.com/wiki/Main_Page The H.P. Lovecraft Wiki]].

For works that reference the Mythos, see the [[ReferencedBy/CthulhuMythos Referenced By]] page.


Thanks to its popularity and its domain status, the Cthulhu Mythos has a large number of crossovers:

* Several stories by Creator/StephenKing
* ''TabletopGame/CthulhuTech'' = (Cthulhu Mythos + {{Mecha}} + PostCyberPunk)
* ''VisualNovel/{{Demonbane}}'' (Cthulhu Mythos + HumongousMecha + {{Moe}}. And by humongous, we're talking about one can destroy the universe with sheer size.)
* The Literature/WhateleyUniverse (Cthulhu Mythos + SuperheroSchool).
* In ''TabletopGame/DungeonsAndDragons'' 3rd Edition, the sourcebook ''Lords of Madness'' states that the Outer Gods (or reasonable facsimiles thereof) are "worshiped" by the inhuman aboleths, while ''Magazine/{{Dragon}}'' #360 implies that Nyarlathotep may be the father of the demon prince Graz'zt.
** 4th Edition hasn't any direct crossovers yet, but it's made clear that the Far Realm referenced in the standard campaign setting is a realm of Lovecraftian horrors that require the combined power of the gods to repel, and is the source of all psionic powers.
** And in the TabletopGame/{{Pathfinder}} (AKA D&D 3.75) campaign setting, a local race of subterranean Abominations explicitly worships the Mythos and use Shoggoths as guards, while the module ''The Carrion Hill Horror'' is pretty much TabletopGame/CallOfCthulhu without the nasty sanity effects, and the ''Rise of the Runelords'' adventures involve the realms of Leng and Kadath. In general, the creators have explicitly said that the non-Earth specific elements of the Mythos are fully compatible with the ''Pathfinder'' universe, and they run with it.
*** Taken to its climax in the 4th bestiary, which includes a Great Old One template and stats for three of them; Hastur (as the King in Yellow), Bokrug, and, of course, the infamous Cthulhu himself.
* A couple of Franchise/DoctorWhoExpandedUniverse {{Tie In Novel}}s have incorporated the Old Ones into the Doctor's universe, to the extent of doing a {{Retcon}} labeling several of the Doctor's past adversaries as Mythos deities under different names. ''All-Consuming Fire'' by Andy Lane adds Franchise/SherlockHolmes.
** According to at least one story, The Nestene Consciousness, leader of the [[DemonicDummy Autons]], is actually one of Shub-Niggurath's oft-mentioned but seldom seen [[ExplosiveBreeder 1000 young]]. Creator/ClarkAshtonSmith would be proud. To be fair, he(?) really does look the part.
* Literature/SherlockHolmes canon, being [[PublicDomainCharacter in the public domain]], has also been bridged more than once, such as in ''Literature/AStudyInEmerald'', ''Sherlock Holmes: The Awakened'' or ''Comicbook/TheLeagueOfExtraordinaryGentlemen''. ''Shadows Over Baker Street'' is an anthology of short stories in which Sherlock Holmes investigates various Lovecraftian mysteries.
* {{Tokusatsu}} show ''Series/UltramanTiga'' drops subtle referrences throughout its run, but it becomes obvious in the two last episodes with a sunken city rising from the ocean and BigBad '''Ghatanothoa''' awakening from its deep slumber.
* ''WesternAnimation/TheRealGhostbusters'' unexpectedly battled Cthulhu in an episode that provides a detailed explanation of H.P. Lovecraft, Miskatonic University, Arkham, and the mythos in general.
* ''Literature/MerkabahRider'' consists of the adventures of a Hascidic Jew who battles demons. However, the overarching story is the invasion of the Outer Gods who are not part of the binary Heaven vs. Hell conflict. The first novel hints that these are Mythos creatures, and this becomes explicit in the second novel. Whether you consider this a crossover depends on whether you see the Rider as his own character, or whether you see it as a Mythos story from the very beginning.
* There's a Franchise/{{Batman}} Elseworlds story called ''The Doom that Came to Gotham''.
** More humorously, Comicbook/{{Hitman}} had the protagonist battling the "Many-Angled Ones'' alongside parody superteam Section 8 thanks to a MadScientist using AlienGeometries in his teleportation experiments.
* Similiarly, Creator/MarvelComics' ComicBook/TheThanosImperative has "Many-Angled Ones", thinly-veiled copies of the Mythos' most popular gods, attacking the MarvelUniverse and even defeating some of the Abstracts, who are among Marvel's most powerful beings.
** Even earlier, Comicbook/DoctorStrange and [[Comicbook/TheTombOfDracula Dracula]] had each battled Mythos-like monsters like Shuma-Gorath and Y'Garon in the 1970s and 1980s, and the first issue of Strange's revived series in 1988 opened with a brief sequence showing him defeating an (unnamed) Cthulhu by causing R'lyeh to sink back beneath the waves.
** Creator/ChrisClaremont also got into the act; in the story where Magneto's HeelFaceTurn begins, Magneto's island base, which he raises from the ocean depths, is very heavily hinted as being R'Lyeh or someplace very similar.
* ''WesternAnimation/SouthPark'' had a trilogy of episodes where BP's drilling opened a hole into another dimension that many {{Eldritch Abomination}}s, including Cthulhu, came through to attack Earth. ''[[VideoGame/SouthParkTheFracturedButWhole The Fractured But Whole]]'' has a boss fight with Shub-Niggurath.
* Let's just say that at one point or another, every major franchise that is even slightly SpeculativeFiction must include a monster that would be right at home in the Mythos.

* Originally the "Cthulhu Mythos". Lovecraft himself jokingly called it 'Yog-Sothothery'.
* Nyarlathotep's often called "Nyarly" or "Gnarly" by his fans.
* "Big C" for Cthulhu.
* "Shubby" for Shub-Niggurath.

!!{{Trope Namer|s}}
* ArkhamsRazor, as a play on OccamsRazor.
* [[DidYouJustIndexCthulhu Anything with "Cthulhu" in it.]]
* GoMadFromTheRevelation, from a line in ''Literature/TheCallOfCthulhu''.
* MotherOfAThousandYoung, the epithet of Shub-Niggurath.
* ThatWhichMustNotBeIndexed, from Lovecraft's "That Which Must Not Be Named".
* TooSpicyForYogSothoth, the Mythos sharing the honor with ''WesternAnimation/TheGrimAdventuresOfBillyAndMandy'' for this one. In the cartoon, Billy is rejected by a [[CaptainErsatz "Yog Sawhaw"]].