This book comprises a complete basic roleplaying game system, a framework of rules aimed at allowing players to enact a sort of improvisational radio theatere only without microphones and with dice determining whe­ther the characters succeed or fail at what they attempt to do. In roleplaying games, one player takes on the role of the gamemaster (or Keeper, in Call of Cthulhu), while the other player(s) assume the roles of player characters (investigators, in Call of Cthulhu) in the game. The gamemaster also acts out the roles of characters who aren't being guided by players: these are called non-player characters (NPCs). From its origin, Call of Cthulhu was designed to be intuitive and easy to play. Character attributes follow a 3D6 curve, and the other Call of Cthulhu mechanics are even simpler. Virtually all rolls determining success or failure of a task are determined via the roll of percentile dice. This means that there's less fiddling with dice of different types, and the concept of a percentile chance of success is extremely easy for beginners and experienced players to grasp. Use this booklet to play Call of Cthulhu immediately, and to discover the improvements to the system. Games rules, an updated character sheet, and a classic adventure are included.