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.

Arkham Horror is a cooperative adventure board game designed by Richard Launius, originally published in 1987 by Chaosium. The game is based on Chaosium's roleplaying game Call of Cthulhu, which is set in the Cthulhu mythos of H.P. Lovecraft and other horror writers. The game's second edition was released by Fantasy Flight Games in 2005, with a third edition in 2018.