The psychological and sociological explorations of intergroup relations have traditionally focused on understanding prejudice and discrimination along a single dimension of social categorization: We study racism and sexism, anti-immigrant attitudes and homophobia, ageism and Islamophobia. What these studies fail to consider is that in real life, each of us belongs to multiple groups. Sociology experiences a boom of research on intersectionality, whereas psychological accounts of consequences of belonging to multiple social groups are still underdeveloped. This dissertation aims to address this gap by investigating attitude formation in situations in which multiple group memberships of a target person are salient, i.e. in multiple categorization settings. Building on social cognition and intergroup relations literatures, I develop a theoretical framework that (1) differentiates between two routes through which group memberships can affect attitudes: ingroup bias and preference for higher status; (2) places perception of similarity as the main cognitive mechanism linking the information about group memberships of others to attitudes towards them; (3) incorporates individual- and societal-level moderators of the effects of group memberships on attitudes. In a series of studies, I demonstrate the difference between the two types of social categories that operate via the two distinct routes. The groups that provide a sense of community and shared norms, such as ethnicity and religion, operate via the preference for ingroup members. The groups that provide information about status of the person, such as education or occupation, affect attitudes directly via preference for higher status, irrespective of own group membership. I show that perceived similarity mediates the link between group memberships and attitudes for both types of groups. Finally, I demonstrate that both individual and contextual factors moderate the relationships between group memberships and attitudes. On the individual level, importance of group memberships to the perceivera s self-concept and perceived threat from the outgroup are associated with stronger ingroup bias. On the societal level, lower country-level acceptance of cultural diversity is associated with stronger preference for ingroup members on cultural dimensions, and lower income and educational inequality is associated with stronger preference for higher-status others on socioeconomic dimensions. This dissertation brings attention to and opens up new avenues for the study of psychological consequences of the complexity of the social worlds we live in
