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. The game was first released in 1981, and eighteen editions (mostly fairly minor revisions) have been published to date. The game makes use of Chaosium's Basic Role-Playing (BRP) system, first seen in the game RuneQuest, but with special rules for Sanity. It is notable among roleplaying games for its longevity and also for remaining largely unchanged for most of its history, with only the most recent seventh edition making significant changes to the rules.
The game takes place in the world of the Cthulhu Mythos, by default in 1920s Lovecraft Country. Popular supplements led to later editions also including the option to play in 1890s England (introduced in Cthulhu by Gaslight), and the modern day (originally the 1980s, introduced in Cthulhu Now). Other supplements, published by Chaosium and others, support other settings, including World War II (Achtung! Cthulhu, also for Trail of Cthulhu), 11th century Europe (Cthulhu Dark Ages), Ancient Rome (Cthulhu Invictus) and the 23rd century (Cthulhu Rising).
- Trail of Cthulhu - a later Mythos-based RPG which uses the GUMSHOE system, focussing on investigation and interpreting clues.
- Delta Green - an alternate contemporary setting based on the Mythos, originally set in the 1990s but later updated.
- Cthulhu Live - a live-action Mythos-based RPG.
- CthulhuTech - a Mythos-based RPG set in the late 21st century, in which humans use advanced technology to fight off Mythos-based threats.