Roleplaying game sourcebook, originally published by Pagan Publishing in the mid-1990s for Chaosium's "Call of Cthulhu" roleplaying game. Written by Dennis Detwiller, Adam Scott Glancy, and John Tynes. It has been one of the most acclaimed RPGs in years, both for its engrossing story and its masterful writing. It is recommended for anyone who likes roleplaying games and for anyone who likes Lovecraftian horror.

While traditional Call of Cthulhu games concentrate on the eldritch horrors of H. P. Lovecraft, "Delta Green" modernizes the Cthulhu Mythos and combines Lovecraftian horror with a modern theme of paranoid conspiracy theory. The players generally play federal law enforcement officers or espionage agents working for a secret government conspiracy known unofficially as "Delta Green" and dedicated to fighting alien threats. 

The extraordinarily grim background posits that humanity has done all the hard work for the Great Old Ones that want to rise from their eternal slumbers and scrape the Earth clean of our kind -- we have been steadily regressing to a baser state and willingly growing more receptive to the madness and despair that the Mythos offers. As a species, we can already see what awaits us -- global slaughter -- but we just don't care. The Great Old Ones have already won, and all we have to do is sit back and watch the show.

Not everyone has given up, of course. Delta Green knows that the Mythos exists and does what it can to stop the chaos, though they know it's almost certainly too late to prevent the end of the world. But they are opposed on many different fronts -- the Mi-Go, fungal horrors from outer space, who engineered the Roswell UFO crash to study and harvest us; Majestic-12, the Men in Black who sold us out to the aliens in exchange for technology and power; the Karotechia, sorcerous Nazis trying to resurrect, both figuratively and literally, the Third Reich; the Fate, a New York criminal syndicate which uses the Mythos to commit crimes; the Shans, mind-controlling insects which are slowly taking over the British government; the Skoptsi, a degenerate Russian cult worshipping a horrifying deity; the surreal, nihilistic forces of entropy and madness embodied in the King in Yellow and the Hastur Mythos; and far too many more...