Identity theory and social identity theory are two remarkably similar perspectives on the dynamic mediation of the socially constructed self between individual behavior and social structure. Yet there is almost no systematic communication between these two perspectivies; they occupy parallel bur separate universes. This article describes both theories, summarizes their similarities, critically discusses their differences and outlines some research directions. Against a background of metatheoretical similarity, we find marked differences in terms of 1) level of analysis, 2) the role of intergroup behavior, 3) the relationship between roles and groups, and 4) salience of social context and identity. Differences can be traced largely to the mi...