The Gamemaster Book begins with technical essays on the Ringworld, from physical construction, to life on the ring, with diagrams. There is a section on the "City Builders"—a Ringworld race that dominated the Ringworld, built floating cities, and sent spaceships to explore other worlds, until a mysterious technological virus destroyed their empire. Another section lists unanswered questions about the Ringworld. There are suggestions for creating scenarios and campaigns, and information on technology of various humanoid species of the Ringworld, and additional rules, including gravity, Credit Rating, and psionics. There is also an introductory scenario ("The Journey of the Catseye") intended to begin a Ringworld campaign. The characters are hired by Captain Gregor Lopez, famous explorer, for a journey to the Ringworld that does not go completely as planned.