[Paraphrased from back cover]
The indispensable tool for the gamemaster to immerse a group of players into the world of HP Lovecraft's Cthulhu.
Here you will find all the secret information about the terrible Cthulhu-Mythos, his banned books, monstrous creatures and powerful gods, cults and dark mysterious places, spells and magical rituals. In addition to the description of how to manage the game successfully, it contains six ready-to-go adventures to start the "cthulhoid" Horror.
To play the game it requires the Cthulhu Player Handbook which contains all rules.