Political psychology focuses upon a diverse range of contexts, including leadership, policy making, nationalism, racism, political extremism, war, genocide, voting, group mobilization and many others. Given the centrality of the social political group in many of these contexts, theories of intergroup relations have proven to be very useful in political psychology research. In attempting to elucidate the origins and mechanisms of discrimination and ingroup favoritism, the Polish-born British social psychologist Henri Tajfel, in collaboration with John Turner and some other European social psychologists, developed Social Identity Theory (SIT) in the 1970s, which has since become one of the most important theories of intergroup relations in social and political psychology. As a Jewish Holocaust survivor, Tajfel had himself witnessed some of the tragic consequences of social identification, ingroup favoritism and outgroup derogation. He returned to his hometown after the Second World War to find that most of his family members had been murdered under the Nazi's genocidal extermination program against the Jews. Tajfel had personally experienced the process whereby people cease to be considered in terms of their individuality in favor of their group membership. In the case of Jews in Nazi-occupied Europe, their categorization as Jews, a highly stigmatized social group membership in the Nazi ideology, resulted in their demonization and mass murder. The evolution of social identity theory was part of a larger movement in the 1960s and 1970s to establish a European social psychology, distinct from the social psychology of the United States. This was a case of scholars, including Henri Tajfel, Serge Moscovici, and Willem Doise, launching a research movement that was political in intentions: establishing an alternative to what they saw as the 'individualistic' and 'reductionist' social psychology of the United States. In addition to launching the European Journal of Social Psychology in 1971, they published a series of books to develop a distinct European social psychology, starting with a kind of manifesto text entitled 'The Context of Social Psychology' (1972). Henri Tajfel, John Turner, and their associates set out to develop a theory that could explain the processes that can culminate in these extreme actions. Although the Social Identity Approach is often deployed as a theory of identity, he intended to develop a theory of intergroup relations. The theory was intended only to explain one aspect of the self, namely that part of "an individual's selfconcept which derives from his knowledge of his [or her] membership of a social group (or groups) together with the value and emotional significance attached to that membership" (Tajfel, 1978, p. 63). Accordingly, it goes without saying that the Social Identity Approach has proven a very useful tool for examining identification with racial, ethnic and national categories, given that these are social categories, as well as intergroup relations in these contexts. In this entry,...