During most of the first half of this century psychologists knew what they wanted to do but had no idea how to do it, and during the second half they have, for the most part, been so preoccupied with how to do it that they have forgotten what they wanted to do. When J. Olds and Milner (1954) announced that rats would stimulate themselves in the septal area, it appeared to open the door to understanding motivation and reinforcement in terms of the underlying physiology. In the ensuing 36 years some progress has been made in that direction, though far outstripped by the progress in methodology. In this review I trace the efforts that have been made to locate the structures involved in self-stimulation by lesions, drugs, determinations of their neurophysiological characteristics, and other more sophisticated methods. I then review experiments, none very recent, comparing brain-stimulation reward to natural rewards and finally indicate how the information so far collected may be incorporated into theories of learning and motivation.