This entry examines the conditions under which group identities become politicized, the psychology underlying this process, and the consequences of political identities for political cohesion and engagement. The political consequences of membership in various demographic and religious groups played a central role in the earliest voting studies and these findings have been theoretically and empirically enriched by an active research focus on social identities within social psychology. Foundational research has identified the underpinnings of cohesive group political behavior in the existence of chronic strong group identities, an established link between the group and politics, and the emergence of group norms fostering a distinct political outlook and political action. Recent research has focused on dynamic aspects of group political cohesion, including threats to the group's status, the convergence of distinct identities, and factors that arouse strong emotions likely to foster collective action. Numerous questions remain unanswered about the conditions under which group political cohesion emerges. One set of questions concerns the origins of chronically strong identities in personality factors such as agreeableness and extraversion. Another set of questions touches on the origins of group identity in situational contexts that promote uncertainty. Finally, the degree to which group leaders can elicit cohesion and conformity, and the situational elements that promote such influence, is a very promising avenue for future research.