The study of culture and related concepts, such as ethnicity and race, in American psychology are examined in this article. First the conceptual confusion and ways in which culture, ethnicity, and race are used as explanatory factors for intergroup differences in psychological phenomena are discussed. Second, ways in which to study culture in mainstream psychology and to enhance hypothesis testing and theory in cross-cultural psychology are illustrated. Finally, the importance of examining sociocultural variables and considering theory in ethnic minority research is addressed. In general, it is proposed that by including theory, conceptualizing, and measuring cultural and related variables, mainstream, cross-cultural, and ethnic research can advance the understanding of culture in psychology as well as the generality of principles and the cultural sensitivity of applications.