First, a number of previous theories of intrinsic motivation are reviewed.Then, several studies of highly motivating computer games are described. These studies focus on what makes the games fun, not on what makes them educational. Finally, with this background. a rudimentary theory of intrinsically motivating instruction is developed, based on three categories: challenge, fantasy, and curiosity.Challenge is hypothesized to depend on goals with uncertain outcomes. Several ways of making outcomes uncertain are discussed, including variable difficulty level, multiple level goals, hidden information, and randomness. Fantasy is claimed to have both cognitive and emotional advantages in designing instructional environments. A distinction is made between extrinsic fantasies that depend only weakly on the skill used in a game, and intrinsic fantasies that are intimately related to the use of the skill. Curiosity is separated into sensory and cognitive components, and it is suggested thot cognitive curiosity can be aroused by making learners believe their knbwledge structures are incomplete, inconsistent, or unparsimonious. The author would especially like to thank Patrick Suppes, his dissertation advisor, and Mark Lepper and John Seely Brown, the other members of his reading committee for their extremely helpful suggestions and continued encouragement. The author would also like t o thank Robert Calfee, Bill Clancey, Allan Collins, Jamey Friend, George Furnas, LauraGould, David Klahr, Tom Moran, Brian Ross, John Sheehan, Ed Smith,'and Mike Williams for helpful suggestions at various stages of this project, Chris Rodriguez for help in performing the experiment in section 3, and the teachers and administrators who gave permission to interview and observe students in their schools.