Call of Cthulhu is a horror fiction role-playing game based on H. P. Lovecraft's story of the same name and the associated Cthulhu Mythos. The game, often abbreviated as CoC, is published by Chaosium; it was first released in 1981 and is in its seventh edition, with licensed foreign language editions available as well. Its game system is based on Chaosium's Basic Role-Playing (BRP) with additions for the horror genre. These include special rules for sanity and luck.

Delta Green is a contemporary era setting for the Call of Cthulhu role-playing game created by Adam Scott Glancy, Dennis Detwiller, and John Scott Tynes, a.k.a. the Delta Green Partnership, of the Seattle gaming house Pagan Publishing. The setting first appeared in a 1992 RPG scenario and revolves around a secretive organization tasked with protecting the United States from paranormal and alien threats. Delta Green combines the classic 1920s Cthulhu Mythos of H.P. Lovecraft with modern conspiracy fiction.