This chapter explores the impact of acculturation on three diverse U.S. populations: Hispanics, represented by a specific focus on Mexican immigrants; African Americans; and Native Hawaiians. It reviews relevant acculturation theories developed to explain cultural and psychological changes occurring in racial and ethnic populations in the United States as a result of interactions with the majority racial/ethnic population. The chapter presents Berry’s model of acculturation in particular, as a helpful theoretical model for clinicians working in neuropsychological rehabilitation to use for understanding psychological issues related to acculturation pressures. It also highlights the unique historical context of acculturation for each ethnic group and its effect on their acculturation experience as well as mental and physical health outcomes. The chapter provides rehabilitation psychologists and counselors with culturally relevant assessment and intervention recommendations for working with ethnically diverse clients.