Interest in the concept of identity has grown exponentially within both the humanities and social sciences, but the discussion of identity has had less impact than might be expected on the quantitative study of political behavior in general and on political psychology more specifically. One of the approaches that holds the most promise for political psychologists is social identity theory, as reflected in the thinking of Henri Tajfel, John Turner, and colleagues. Although the theory addresses the kinds of problems of interest to political psychologists, it has had limited impact on political psychology because of social identity theorists' disinclination to examine the sources of social identity in a real world complicated by history and culture. In this review, four key issues are examined that hinder the successful application of social identity theory to political phenomena. These key issues are the existence of identity choice, the subjective meaning of identities, gradations in identity strength, and the considerable stability of many social and political identities.