[[caption-width-right:350:Welcome to your new job, rookie.]]

->''We travel light, we probe deep, and we strike hard. We're Delta Green, and we may be outlaws and cowboys and fools, but we've kept this green ball of shit safe and sound for longer than most people have been alive.''
--> -- '''Reginald Fairfield'''

->''[[Literature/{{Trainspotting}} Choose]] federal law enforcement. Choose the military. Choose NASA or the CDC. Choose lying to your superiors. Choose to ruin your career. Choose no friends. [[TheMasqueradeWillKillYourDatingLife Choose divorce]]. [[DrowningMySorrows Choose life through the bottom of a bottle]]. Choose destroying evidence and [[ShootTheDog executing innocent people]] [[HeKnowsTooMuch because they know too fucking much]]. Choose black fatigues and matching gas masks. Choose an [=MP5=] stolen from the CIA loaded with Glasers, with a wide range of fucking attachments. Choose blazing away at [[EldritchAbomination mind numbing, sanity crushing things from beyond the stars]], [[SanitySlippage wondering whether you'd be better off stuffing the barrel in your own mouth]]. Choose The King In Yellow and waking up wondering who you are. [[AteHisGun Choose a 9mm retirement plan]]. [[DrivenToSuicide Choose going out with a bang at the end of it all]], PGP encrypting your last message down a securely laid cable as an NRO Delta wetworks squad busts through your door. Choose one last Night at the Opera. Choose Delta Green.''
--> -- '''Anonymous'''

An acclaimed sourcebook for the famous TabletopGame/CallOfCthulhu tabletop roleplaying game, Delta Green tells the story of the eponymous organization, a secret United States agency born of the Federal raid on [[TownWithADarkSecret Innsmouth, Massachusetts]] in 1929 and tasked to protect the country from paranormal threats. After an operation gone horribly wrong in Cambodia in the '60s, Delta Green was officially shut down -- but its leaders, aware of the things lurking in the cracks of reality, continued the fight illegally, stealing resources from the government, carefully picking new members from the federal agents community, and generally acting like rightfully pissed off {{Cowboy Cop}}s in their battle against the supernatural. It would not be until the 1994 assassination of Major General Reginald Fairfield, Delta Green's ''de facto'' leader, than DG would take up their current incarnation: a deeply hidden conspiracy in the labyrinthine world of the United States federal agencies, structured in semi-independent cells.

The new Delta Green was released in 2016 and advanced the plot. After a series of operations against the Mi-Go and the Greys, Delta Green delivers a huge blow on MAJESTIC-12, in 2001 the 9/11 attacks results in a total reorganization of the US intelligence community. Delta Green is reactivated, brought back into government fold, given a proper budget and using TheWarOnTerror as their new cover, this new organization is nicknamed "The Program". Some old members refused to go official and decided to keep the old group running, nicknamed "The Outlaws", this group acts more like the old Delta Green, as a illegal and unauthorized conspiracy.

Delta Green is heavily based on classical conspiracy/UFO theories, meshing them with the Franchise/CthulhuMythos milieu: DG themselves are a spin on TheMenInBlack, but there are also other shadow agencies involved, including the now famous Majestic 12 group that deals with the Greys (actually Mi-Go in disguise). Other players are the Karotechia, [[{{Ghostapo}} occultist Nazis serving an "ascended" Hitler]]; the Fate, a criminal organization that makes heavy use of Mythos creatures and spells for fun and profit; [=SaucerWatch=], a naïve yet well-funded UFO research group that may be closer to the truth than they know; and the [[AncientConspiracy Cult of Transcendence]], among others.

The tone of the book is even [[CrapsackWorld bleaker]] than standard [=CoC=]: where the basic game has investigators struggling against Mythos creatures and the cultists that serve them (and DG does include its fair share of battle against these forces) the primary adversaries are evil and/or utterly amoral humans that (attempt to) use the forces of the Mythos for their own benefit, and are becoming as amoral as them. The Stars are Coming Right, and there may not be anything that Delta Green, or anyone else can do about it...

[[DefiantToTheEnd But it doesn't mean they have to make things easy for them.]]

For the ''other'', ''slightly'' less depressing, ''slightly'' funnier Lovecraft-meets-spy-fiction setting, see ''Literature/TheLaundryFiles''.

In late 2015, a kickstarter was held for a new series of Delta Green sourcebooks. It reached 10 times its expected goal for a total of $300,000 recieved, and new material is expected throughout 2016. The creators have released a PDF copy of a quick start guide, ''Need to Know'' for free on their [[http://www.delta-green.com/2016/02/download-delta-green-need-to-know/ official website.]]

!!This game provides examples of:

* TheNineties: The setting of the original sourcebook.
* AliensAndMonsters: And not all of them are [[CombatTentacles betentacled.]]
* AncientConspiracy: Both averted and played straight with the Cult of Transcendence. As the Alta Vendita, they've been around since the Crusades, but they underwent a significant change in leadership and purpose after the First World War showed them how much their attempts at running the world had failed. [[ScamReligion The book giving their background also leaves open the possibility that the entire history of the Cult as laid out is a lie meant to impress new initiates with conspiratorial leanings]].
* ArgentinaIsNaziland: The [[{{Ghostapo}} Karotechia]], Hitler's occult division whose remnants are hiding in the Amazon.
* AscendToAHigherPlaneOfExistence: ''Through A Glass Darkly'' features a machine that can allow a person to do this.
* AllTherapistsAreMuggles: Agents can go to the therapist after an operation to attempt to recover [[SanityMeter Sanity points]]. There are two choices: Get treatment but lie about the unnatural, which is a more safe option although it gives less SAN points back, or tell the horrible truth to the therapist. However, if you succeed this will be a SubvertedTrope as the therapist will not only believe you, himself ''will lose sanity points''.
* BrainFood: Agent NANCY is DG's foremost forensic analyst and autopsy expert. [[spoiler: She is, in fact, a [[ImAHumanitarian ghoul]], and can obtain knowledge from dead bodies by devouring their brains. All ghouls apparently have this ability.]]
** The Karotechia's Reinhard Galt also has this ability, learned from the Anziques.
* BadassNormal: Many [=NPCs=], such as the late Major Fairfield, Captain Forrest James or MJ-12's Adolph Lepus. The [=PCs=] can also become this.
* BroadStrokes: According to the official site, nothing in Delta Green is canon. Instead, they encourage players to use whatever works for their game.
** With regards to the original ''Call of Cthulhu'' RPG which DG was an expansion for, they change some facets of the gods and monsters. Most notably, Hastur is dramatically different from the more Derleth-inspired ''Call'' version. Overall, Delta Green considers Lovecraft's works "canon", and the stories of other Mythos writers depending on the needs of the plot.
* ChurchOfHappyology: The Enolsis Foundation. In this setting, of course it has a [[DarkSecret horrible secret]].
* CodeName: Every DG agent has one. Also, there are the MJ-12 projects, and the various classified documents used throughout the game.
* CosmicHorrorStory: Even without all the human cultists, sorcerers and others dealing with Mythos forces, humanity would be in pretty deep trouble. ''With'' them around, though, they're utterly screwed.
* ClarkesThirdLaw: Delta Green calls magic ''Hypergeometry'', due it's frequent association with lines, shapes, numbers, position and mathematics. The game gives example on how a tribal shaman drawing a mandala in sand or a scientist pointing lasers in the sky to invoke something begin similar things with a similar "math", and the rituals are described to be "tapping" in an infinite energy grid beyond the four dimensions. ''Hypergeometry'' is stated to be the "technology" used by advanced alien and unearthly species such as the Elder Things, Mi-Go and the Great Race of Yith, and implied they were passed down to humanity by the [[EldritchAbomination Great Old Ones]].
* CrapsackWorld: The world is full of Lovecraftian darkness. And doomed.
* DarkIsNotEvil: Ghouls have a bit of that vibe going on, depending on the particular group or individual. Of course, players shouldn't rely on it too much unless they want to become lunch.
* DarkerAndEdgier: DG is like a grimdark X-Files, although the initial ''Convergence'' scenario was first printed before that show premiered.
* DeadlineNews: ''Phenomen-X'', the basic cable conspiracy investigation show, can suffer this. DG is perfectly willing to treat them as canaries in the coal mines to see if the alleged supernatural is actually a threat.
* DidYouJustFlipOffCthulhu: It can be argued that this is the best DG can hope to do.
* DownerEnding: Delta Green fights the fires it sees, but it's all going downhill. Some modern [=CoC=] material hints at possible evacuation to space habitats or the Dreamlands, but nothing positive or canonical.
** [[spoiler: The Delta Green short story "After Math" details the end of the world through the eyes of an elderly Delta Green agent.]]
* EldritchAbomination: Naturally. The "definition" of Great Old Ones is as follows:
--> "The Great Old Ones came from elsewhere and fought over the Earth billions of years before man, and now sleep in some infernal cycle of time. Life on Earth is the result of biological runoff; a fungus borne of alien shit, that has clung and crawled and evolved as these giants sleep. Their science is our magic, and remnants of their civilizations spring up to infect our world. Soon, they will wake and destroy humanity. NOTHING can stop this."
* FaceStealer: Multiple examples. Ghouls are particularly inclined to do this.
* {{Ghostapo}}: The Karotechia -- at least, what remains of it. An eldery worshipper of Yog-Sothoth, an undead MadScientist {{Necromancer}} mixing the legacies of both [[Literature/HerbertWestReanimator Herbert West]] and Dr Munoz from ''Cool Air'', a [[ImAHumanitarian humanitarian]] ubermensch who gets immortality and invincibility in the bargain, and the "ascended" spirit of Adolf Hitler (at least, they ''think'' it's Hitler...)
** The real Hitler ordered the former Karotechia to summon Azathoth, in an attempted TakingYouWithMe against the entire world.
* GoMadFromTheRevelation: Let's just say that the suicide rate in Delta Green is above average.
* TheGovernment: Many real-life US Federal agencies are provided for [=PCs=] to be part of, from familiar ones like the FBI and the DEA to the more obscure like [=FinCEN=] or the National Security Council. ''Countdown'' extends the roster to a number of foreign agencies.
* GovernmentAgencyOfFiction: From DG and MJ-12 to equivalents in other countries, like the British PISCES.
* GovernmentConspiracy: Majestic 12. Delta Green itself used to be this.
** Alternatively, if you believe one Delta Green Agent: "We're the government conspiracy. Those guys are just the government".
** PISCES can be considered a variation as well [[spoiler:considering that it's been taken over wholesale by the Shan.]]
* TheGreys: The high-tech aliens cutting secret deals with MJ-12 for fun and profit. Of course, [[spoiler:they are not what they seem.]]
* GroinAttack: The Skoptsi sect in Russia does this to themselves -- all members of the cult must undergo castration.
* GutFeeling: The reason the Mi-Go are so interested in humans is our (to them) unnerving capability to extrapolate accurate answers with little information and no clear logic chains of thought.
* InfectiousInsanity: One of the plots of MJ-12's Project OUTLOOK is to create a "psychological virus", a way of causing a cascading spiral of riots and unrest through manipulation of the media.
** [[spoiler:Hastur. Unlike vanilla ''Call of Cthulhu'', Hastur is not a God or Old One, but an infectious and pervasive force of decay. Knowing about Hastur or its related mythos trappings allows such decay to happen on a person's psyche.]]
* InterserviceRivalry: All the time between the various real-world agencies. Delta Green and MJ-12 used to have this in the short period where both officially worked for the US government.
** The new sourcebooks feature ''two'' Delta Greens; the Special Access Program, a reactivated, officially sanctioned version, and "the Cowboys", DG Agents who refused to come in from the cold and thus operate as vigilantes.
* JustBeforeTheEnd: In some level, everyone knows that there is not much time left for humanity. [[spoiler:This is why the Mi-Go created the Grey deception: to extract as much information as possible from humans before our time runs out.]]
* KnightTemplar: Delta Green agents used to go too far in their quest to both protect the American populace from the supernatural and keep the existence of the latter (and itself) a secret, particularly in the Fairfield era. Some still do.
** In the words of one DG agent, "we do the horrific to prevent the apocalyptic". Later in that story, the same agent deliberately, and (we are led to believe) needfully, shoots a baby.
* KnowWhenToFoldEm: The Deep Ones. In the original sourcebook, it's noted that DG invested much of its efforts from its founding in the wake of Innsmouth until after World War II to hunting down Deep One colonies. As such, the vast majority of them have determined the surface world is now more trouble than it's worth, and only very isolated enclaves remain on the surface.
** [[spoiler: The creators have alluded to this being the fate of the Mi-Go; they, through the Greys, stopped working with Majestic-12 around the turn of the millennium.]]
* TheMafia: The Fate is New York City's magic-using organized crime cartel.
* MakeWayForTheNewVillains: A new sourcebook will feature new threats arising from / with the Global War on Terror, with many old threats no longer relevant. Several other books funded via Kickstarter will deal with what happened to the old threats; including MAJESTIC-12, PISCES, and The Fate.
* TheMasquerade: Delta Green fights to keep the existence of the paranormal a secret from the public at large. Sometimes, that involves [[HeKnowsTooMuch ''neutralizing'' innocents.]]
* MindScrew: The Hastur Mythos. Also SurrealHorror.
* NoSuchAgency: Delta Green started off as an official one. Now it exists in two forms; as a highly classified and secret interservice program, and as an unauthorized, unofficial conspiracy. The 2016 brought Delta Green back as an "official" organization nicknamed "The Program".
** MAJESTIC-12 is a bit more "oficial" then DG, with proper government recognizement.
** The original sourcebook classifies the real-life intelligence agency [[https://en.wikipedia.org/wiki/National_Reconnaissance_Office National Reconnaissance Office]] as one, at the time of the writing (1996) the US government neither denied or confirmed the existence of the NRO and most of the operations that the NRO were off the books, because of that the NRO runs the "NRO section DELTA", a black ops assassination group used by MAJESTIC-12 as their own hit squad. As HistoryMarchesOn, most details about NRO were declassified and revealed, this became a DiscreditedTrope and in the 2017 edition the NRO was DemotedToExtra.
** Some other foreign organizations similar to Delta Green include: M-EPIC of Canada, PISCES of the United Kingdom and GRU SV-8.
* PsychicPowers: There are a few optional rules for those; PISCES is the most knowledgeable about the subject.
* PsychoForHire: Adolph Lepus.
* PuppeteerParasite: The Shan, of course.
** The Mi-Go can assert mental control over anyone infected with protomatter; however, ''Convergence'' notes they tend not to use this ability.
* PyrrhicVictory: This is the absolute, insanely-optimistic, ridiculously-unlikely ''best'' outcome of humanity's struggle. The more likely outcomes [[ApocalypseHow are]] [[EarthShatteringKaboom much]] [[TheEndOfTheWorldAsWeKnowIt worse]].
* RenegadeSplinterFaction: Following their disbandment, Delta Green for the U.S. government. However, their ruthless actions are partly justified.
** In the new setting, after 2001, Delta Green succesfully dismantled MAJESTIC-12 and it's remnants were fusioned into a new, unified and official Delta Green. Some old members of DG weren't very happy with this and decided to form it's own faction, that also calls itself Delta Green. The "official" Delta Green is called "The Program" and the "renegade" is called "The Outlaws".
* LaResistance: The Army of The Third Eye, against the Shan.
* RockMeAsmodeus: Charnel Dreams is one of the most popular bands in New York City. Their lead singer is the head assassin for the Fate, worships Nyarlathotep, and works Cthulhu Mythos spells into the lyrics of his songs.
* SacrificialLamb: "Friendlies" are those people that support DG's cause but are not fully inducted into the conspiracy. Delta Green maintains a database with full information on each and every one, so that they can be properly "taken care of" if the need arises.
* ShownTheirWork: The bibliography shows a respectable collection of material regarding world history, UFO folklore, and the praxis of the US intelligence community.
* TheSociopath: Adolph Lepus, literally, as he has an antisocial personality disorder.
* SanityMeter: Naturally as a TabletopGame/CallOfCthulhu game. ''Delta Green'' offers an interesting variation: The 2016 standalone adds ''bonds'' for every agents. Every agents starts with points in each bond, Agents can "''project''" on their bonds to lower the SAN loss although in the coast of the relationship with the bonds, there are other ways you can also loss relation with bonds such as commiting illegal actions.
* SpyFiction: Stale beer flavored.
* TakingYouWithMe: Reginald Fairfield's last stand.
* UnderNewManagement: In the updated setting, "The Program" was born out of a takeover of MAJESTIC by Delta Green agents.
* UsefulNotes/TheVietnamWar: An unsanctioned operation in that time and its disastrous aftermath is what made the US government dissolve Delta Green.
* ThoseWackyNazis: The Karotechia.
* UsefulNotes/TheWarOnTerror: A new standalone RPG has been funded on kickstarter, with the goal of updating the Delta Green setting to the modern day, with the War on Terror serving as a backdrop for altered powers of federal law enforcement (including the reactivated Delta Green "Program").
* WellIntentionedExtremist: The Army of the Third Eye are mostly crazed fanatics, but what they fight against is much worse. Delta Green itself can come off as this at times.
* WorldOfChaos: The Hastur Mythos suggests this as an effect of its influence; reality becomes relative to the observer, buildings gain new floors at night, time flows differently. This goes double for Carcosa, the land "governed" by the King in Yellow.
* TheWorldIsAlwaysDoomed: Delta Green's unofficial mission is to "delay the inevitable for ''a few more years''" (emphasis ours). They've been at it for the better part of a century.