This chapter discusses the psychological and societal processes involved in the phenomenon of multiculturalism. An emphasis is placed on reviewing and integrating relevant findings and theories stemming from cultural, personality, and social psychology. The chapter includes sections devoted to defining multiculturalism at the individual, group, and societal level, discussing the links between acculturation and multiculturalism, how to best operationalize and measure multicultural identity, the issue of individual differences in multicultural identity, and the possible psychological and societal benefits of multiculturalism. The chapter concludes with a discussion of future challenges and needed directions in the psychological study of multiculturalism.