In its original incarnation, Delta Green was a supplement to Chaosium's Call of Cthulhu, the popular 1981 RPG based on H.P. Lovecraft's fiction. The name Delta Green refers to a group within the setting, itself named after a now-obsolete clearance level in US military intelligence. The group was introduced in the seventh issue of The Unspeakable Oath fanzine, in early 1993. The consolidated setting book, named simply Delta Green, won the Origins Award for Best Roleplaying Supplement on its release in 1997. Delta Green is a product of Pagan Publishing.
The setting is innovative, bringing the Cthulhu Mythos firmly into the modern era without cutting corners. Lovecraft's bleak canon is central; this is not the comedy of The Laundry or the high-concept action of CthulhuTech. This is a game of horror.