Groups exist in a time environment. The group develops, changes, may function for years, and eventually disbands. The theory of groups across time is in a different psychological domain than that of short-term groups. For example, in long-term groups changes in group membership are inevitable whereas in short-term groups these changes are rarely experienced. As a result the time perspective of the group members becomes salient, calls for maintaining a state of equilibrium, and necessitates dealing with strategies of changing membership. Three of the central concepts in long-term groups include continuity (A sense of the relation among the past, present, and future of the group), images of the future, and attachment. The implications of this orientation for theory and research are elaborated.( Author)