Polyculturalism is an ideology focusing on the many ways that racial and ethnic groups have interacted, exchanged ideas, and influenced each other's cultures throughout history and into the present. In this paper, we first briefly review the introduction of and research on polyculturalism by historians. Then we summarize numerous studies with racially and ethnic diverse college students and adult community members in the United States, which have found that greater endorsement of polyculturalism is significantly associated with more positive racial/ethnic intergroup attitudes (less support for social inequality, greater interest in, appreciation for, and comfort with diversity and differences, greater interest in intergroup contact, and greater support for liberal immigration and affirmative action policies) and lower sexual prejudice (lower affective prejudice toward gay men and lesbians, traditional heterosexism, and denial of discrimination against homosexuals, and more positive attitudes toward gay men and lesbians). We conclude by discussing several future directions of this work.All of us, and I mean ALL of us, are the inheritors of European, African, Native American, and even Asian pasts, even if we can't exactly trace our blood lines to all of these continents. (Kelley, 1999; p. 81) Culture cannot be bounded and people cannot be asked to respect 'culture' as if it were an artifact, without life or complexity. Social interaction and struggle produces cultural worlds, and these are in constant, fraught formation. Our cultures are linked in more ways than we could catalog, and it is from these linkages that we hope our politics will be energized. (Prashad, 2001; p. 148) Each of these quotations from historians Kelley and Prashad captures "polyculturalism", which is an ideology focusing on the many ways that racial and ethnic groups have interacted, exchanged ideas, and influenced each others' cultures throughout history and into the present. In this paper, we briefly trace through the introduction of and research on polyculturalism by historians and then describe recent social psychological research findings from a series of studies in the United States examining the associations that endorsement of polyculturalism has with intergroup attitudes, including racial/ethnic attitudes and sexual prejudice. We suggest that the continued interdisciplinary study of polyculturalism will add to a fuller understanding of intergroup attitudes and relations.