Group formation includes the short-lived emergence of ephemeral groups, the self-organization of people into more enduring new collectives, and the deliberate assembly of new groups by powerful outsiders. Behavioral coordination among two or more individuals creates an ephemeral acting group. In more persistent groups that come together over multiple interactions, the forming process establishes the roles, norms, and boundaries that constitute group structure. Structure is a feature of standing groups, to which members continue to belong even when the group is not assembled for action. Structures established during group formation guide behavior when members assemble and reassemble over time.

In standing groups, successful group formation creates psychological bonds between members and the group. When groups are deliberately assembled, as when a teacher assigns students to project ...