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 in-group 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, in-group favoritism, and outgroup derogation. He returned to his hometown after World War II to find that most of his family members had been murdered under the Nazis’ 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.