Interpersonal interactions encompass a wide range of communication perceptions and behaviors that involve a process whereby individuals exchange verbal and nonverbal messages in different types of relationships (family, friendship, professional, and acquaintance) throughout the life span. Interpersonal [Page 1181]interactions function to construct, manage, and define the power and affective dynamics of the relational world to meet changing instrumental and affective needs as individuals age. This entry focuses on the changing nature and function of interpersonal interactions through prebirth–infancy, childhood, adolescence, emerging adulthood, adulthood, and older adulthood. Emphasis is placed on the complex dynamics of changing communicative competencies and the complexities of the interactive/relational world.