The personal and political significance of social identity is well studied; this paper contributes to those studies a discussion of the metaphysics of identity. Three features of an adequate theory of identity are specified, two existing theories are considered, and concerns about them are leveraged in order to craft a new theory. An identity group is a group whose members value and commit to valuing enough of the activities and products of cultures associated with the group. Theories of culture and (...) commitment are provided. Some hard cases are discussed. (shrink)