Few behavioral processes are more central to the development and maintenance of intimate relationships than the communication of affection. Indeed, affectionate expressions often initiate and accelerate relational development. By contrast, their absence in established relationships frequently coincides with relational deterioration. This text explores the scientific research on affection exchange to emerge from the disciplines of communication, social psychology, family studies, psychophysiology, anthropology, and nursing. Specific foci include the individual and relational benefits (including health benefits) of affectionate behavior, as well as the significant risks often associated with expressing affection. A new, comprehensive theory of human affection exchange is offered, and its merits relative to existing theories are explored.