(from the chapter) This chapter describes the historical development, metatheoretical background, and current state of the social identity perspective. The theory developed as an analysis of intergroup relations among large-scale social categories and has evolved a strong social cognitive emphasis. In this chapter, we show that the social identity perspective is intended to be a general analysis of group membership and group processes that focuses on the generative relationship between collective self-conception and group phenomena. We describe several applications of the social identity perspective to small groups including: differentiation within groups; leadership; deviance; group decision-making; computer-mediated communication; mobilization, collective action, and social loafing; and group culture. We conclude with a discussion of the strengths and weaknesses of the perspective and of future directions