J. R. Kantor (1888-1984) did not achieve the prominence of his contemporaries, such as John B. Watson and B. F. Skinner. However, he established the most naturalistic and conceptually systematic psychology since Aristotle. Today, his interbehavioral psychology is consistent with converging movements in the naturalization of the behavioral, developmental, social, and cognitive sciences. Kantor, his interbehavioral psychology, and these movements are the focus of this text.