Two studies were designed to validate a measure of American identity for use with diverse ethnic groups. The American Identity Measure (AIM) was created by adapting the Multi-Group Ethnic Identity Measure (MEIM) to refer to exploration and affirmation of individuals' identification with the United States. In Study 1, students from nine U.S. universities (N = 1,773) completed the AIM and the MEIM. Confirmatory factor analyses indicated that the AIM fit the data well and that the factor structures of ethnic and American identity were equivalent. In Study 2 students from 30 U.S. universities (N = 10,573) completed the AIM, a comparison measure of American identity drawn from recent qualitative work, and measures of American cultural practices and individualist values. The factor structure of scores generated by the AIM was equivalent across ethnicity and immigrant generation, and latent mean scores on the AIM were only modestly different across ethnicity and immigrant generation. Whites and later-generation immigrants scored higher on American identity affirmation; Asians and first-generation immigrants scored lowest. The AIM was strongly correlated with the comparison measure of American identity (suggesting convergent validity) and with American cultural behaviors (suggesting construct validity). American identity was only weakly associated with individualist values, perhaps implying that American identification may not be as closely intertwined with rugged individualism as previously thought. These results are discussed in light of the availability of American identity for individuals from various ethnic backgrounds as well as the implications of national identity for intergroup relations.