Individuals act differently within the political process; behavior can range from passive acceptance of a situation to violent riots. This chapter outlines various theoretical explanations as to why these differences in behavior occur and what psychological processes mediate them. In the social psychological explanations of collective political protest the emphasis has changed in recent years. Traditional theories concerned individual decision making processes whereas more recent research has focused on the intergroup context of the political environment. This chapter concentrates on the three currently predominant approaches; expectancy-value theory ([e.g. Walker & Mann, 1987e.g. Klandermans, 1997), relative deprivation theory (e.g. Walker & Mann, 1987) and social identity theory (e.g. Tajfel & Turner, 1979). It considers recent research that attempts to integrate these approaches with each other (Simon, Loewy, Sturmer, Weber, Freytang, Habig, Kampmeier & Spahlinger, 1998; e.g. Kawakami & Dion, 1995), and we conclude by presenting a study that suggests collective efficacy is an important motivator of collective action, but that social identification moderates this relationship, thereby acting as a crucial psychological platform for collective action.