Recent theorizing and research has attempted to explicate the functions of moods and emotions within small groups. In this paper, we examine these areas and suggest that affect in groups, as well as specific mechanisms to regulate and maintain certain affective states in groups, have had important roles in promoting group survival over evolutionary history. Specifically, we suggest that affect in groups serves a coordination function, which can take one of two forms. First, affect in groups quickly provides information about the environment and group structure to other group members, thus coordinating group activity via a communication function. Second, shared affect in groups coordinates group activity through fostering group bonds and group loyalty. These two functions of affect in groups are closely related and mutually reinforcing. Current research and directions for future research within an evolutionary perspective are also discussed.