Mental imagery is an important component of mental life, and an understanding of imagery will facilitate the use of it in therapy. In particular, the "systematic desensitization" therapies used to cure phobias often use imagery, and these techniques will be enhanced by a fuller understanding of how imagery operates. In addition, an understanding of how the brain produces mental images in normal people will increase our understanding of the brain itself, and eventually will put us in a position to study what has gone wrong with the brain when imagery abilities are disrupted following a stroke. One of the most fundamental observations about mental images is that we do not have them all of the time. Most previous research on imagery representation has focused on the kinds of operations that can be performed on an image once it is in active memory (e.g., rotating, scanning, and bending imaged objects). The present research focuses on our ability to generate mental images, to evoke them from stored information. The research is cast within the "computational" framework recently developed by Marr (1982), with the goal of understanding the nature of the computations that produce images well enough to be able to program a computer to mimic these mental events. This goal is pursued in experiments that investigate the nature of the input to the computations, the output from them, and the structure of the computations themselves. The experiments on the nature of the input examine the relationship between the representations that are used to generate a mental image and those that are used to recognize objects in perception. One theory is examined in detail, which has been proposed as a way to program computers to recognize objects. The experiments investigating the nature of the output examine the plausibility of the "array" representation, in which images are depictions of objects. Finally, the experiments on the computations themselves examine how sets of computations work together to accomplish different aspects of the generation process.