My dissertation explores the realistic dimensions of the cultural threats posed by immigrants and their impacts upon Americans' immigration policy preferences. Cultural threat, at present, is an under-theorized concept within the opinion research on immigration. The existing literature conceptualizes the cultural threats posed by immigrants largely in terms of social identity and symbolic politics theories, where immigrants are cast as posing a collective level threat to the American identity and its related symbols. What remains largely under-developed is a theoretical and empirical exploration of the more tangible and realistically rooted cultural threats posed by immigrants to individual native born citizens. In this dissertation, I draw upon the literature on acculturation and adaptation originating within the fields of cultural anthropology and cross-cultural psychology, as well as social psychology research on intergroup anxiety and language-based social exclusion, to derive a theory of the realistic and personal cultural threats of immigration. Three forms of realistic cultural threat will are explicated and empirically explored: (1) residing in a local context undergoing substantial and unprecedented influxes of immigrants, (2) contact with unassimilated immigrants within one's neighborhood, and (3) exposure to foreign language in interpersonal and impersonal circumstances.