Call of Cthulhu 7th Edition - Rules of Play says:
Call of Cthulhu is a roleplaying game based around the incredible works of H. P. Lovecraft. Playing the role of steadfast investigators, you travel to mysterious and dangerous places, unravel vile plots, and stand against the ancient horrors of the Cthulhu Mythos. You will encounter insanity-endusing entities, monstersolder than time, and insane cultists, all of which you must overcome as the fate of the world rests on your shoulders.
The Keeper Rulebook, contains the core rules, background, guidance, spells, and monsters of the game. It is used by the Keeper of Arcane Lore (the game master) who will use it toguide the other players thourght the adventure!
Call of Cthulhu 7th Edition Review:
Don't just take our word for it, check out this review of Call of Cthulhu 7th Edition!