This article presents a model of social identity development and integration in the self. Classic intergroup theories (e.g., social identity theory, self-categorization theory) address the situational, short-term changes in social identities. Although these theories identify the contextual and environmental factors that explain situational changes in social identification, the intraindividual processes underlying developmental changes in social identities and their integration within the self remain to be identified. Relying on recent intergroup models as well as on developmental (i.e., neo-Piagetian) and social cognitive frameworks, this article proposes a four-stage model that explains the specific processes by which multiple social identities develop intraindividually and become integrated within the self over time. The factors that facilitate versus impede these identity change processes and the consequences associated with social identity integration are also presented.