This chapter deals with three broad issues: Whether emotions are epiphenomenal, how emotions play a crucial role in determining appraisal processes, and what the mechanisms are by which emotions may influence interpersonal behavior. We present evidence from studies indicating that emotions play a crucial role in the regulation of social behavior. Social regulation by emotion is particularly clear in a process we call social referencing—the active search by a person for emotional information from another person, and the subsequent use of that emotion to help appraise an uncertain situation. Social referencing has its roots in infancy, and we propose that it develops through a four-level sequence of capacities to process emotional information from facial expression. We discuss whether the social regulatory functions of emotion are innate or socially learned, whether feeling plays an important role in mediating the effects of emotional expressions of one person on the behavior of another, and whether stimulus context is important in accounting for differences in reaction to the same emotional information.