This publication is one of a series of information booklets for the general public published by the United States Atomic Energy Commission. Among the topics discussed are: How Reactors Work; Reactor Design; Research, Teaching, and Materials Testing; Reactors (Research, Teaching and Materials); Production Reactors; Reactors for Electric Power Generation; Reactors to Supply Heat; Reactors at Sea; Reactors in Space; Reactor Safety; and Reactors of Tomorrow. The appendix contains a list of United States Central Station Nuclear Power Projects that are operable, being built, or planned as of June 1970. A list of suggested references, including books, reports, articles, and motion pictures, is included. School and public libraries may obtain a complete set of the booklets without charge. (BT)