is a process which usually either informally or formally accepts members into its ranks granting them membership. Groups such as this include- societies, clubs, teams, cliques and political parties.

A small group of individuals in which the individual is phychologically and formally a member. A fraternity, the Rotary Club, or a bowling team are examples of membership groups. It is those groups in which the individual has direct, face-to-face psychological relations and interdependence with other members.

Membership groups: are the groups to which the individual already belongs and provide parameters within which individuals make purchasing decisions, whether individuals are conscious of it or not.