Roger T. Kelleher, rightly known as one of the foremost contributors to behavioral pharmacology, also made many important contributions to the experimental analysis of behavior. He participated significantly in the development of the discipline, through both his research and his editorial contributions to this journal. This article summarizes his contributions to the field of behavior analysis. His most significant empirical and conceptual contributions to behavior analysis came in two domains--conditioned reinforcement and the power of schedules of reinforcement. His accomplishments in these two domains still serve as principal foundations for modern research and theory. (Contains 10 figures.)