This paper focuses on research that has implications for two important components to self-identity: personal identity and social identity. Three questions are addressed: (1) How do people derive a unitary sense of self out of membership in many different social categories such as those of age, gender, race, and social class? (2) Do people respond differently when the social as opposed to the personal aspects of their identity are evoked? (3) How do people respond to collective injustice? A major theme in the results is that, although the social component of self confronts the individual with fundamental problems, the need for a shared identity motivates people to maintain this dimension of self despite the problems it generates.