An organization has a relatively identifiable boundary. This boundary can change over time, and it may not always be perfectly clear, but a definable boundary must exist in order to distinguish members from nonmembers. It tends to be achieved by explicit or implicit contracts between members and their organizations. In most employment relationships, there is an implicit contract where work is exchanged for pay. In social' or voluntary organizations, members contribute in return for prestige, social interaction, or the satisfaction of helping others. But every organization has a boundary that differentiates who is and who is not part of that organization.