Horror roleplaying game set in the milieu of H.P. Lovecraft's stories. There have been many editions and licensed products for the setting.
The first edition of Call of Cthulhu was published in 1981, using a simplified version of the Basic Role-Playing system used in RuneQuest. It is currently up to the 6th edition and there are spin off settings such as Cthulhu Now, Gaslight, Delta Green, Dreamlands.
The core mechanics have changed very little over the six editions, making all materials more or less compatible with all editions.