Assessment research on ethnic minorities presents multiple methodological and conceptual challenges. This article addresses the difficulties in denning and examining ethnicity as a variable in psychological research. The authors assert that many of the problems stem from not making explicit the assumptions underlying the use of ethnicity as an explanatory variable and from inadequately describing cultural and contextual characteristics of ethnic minority samples. Also raised are common methodological problems encountered in examining race, ethnicity, and culture in assessment research, such as decisions regarding which populations to study, sampling methodologies, measure selection, method of assessment, and interpretation of results. Finally, some guidelines are offered for tackling some of the methodological dilemmas in assessment research with ethnic minorities. Assessment research on ethnic minority groups has had a controversial history. For example, comparisons of intellectual abilities and cognitive skills, of self-esteem and self-hatred, of personality patterns, and of prevalence rates and degrees of psychopathology among different ethnic and racial groups have generated considerable controversy regarding the validity of findings. It is our belief that conducting valid assessment research with ethnic minority groups is particularly problematic because of methodological, conceptual, and practical difficulties that arise in such research. This article addresses common methodological problems that have plagued assessment research on ethnic minorities. Our intent here is not to provide definitive solutions to methodologica l problems but rather to raise issues that many researchers may not have otherwise considered, so that informed decisions can be made about how to handle variables related to ethnicity. We also pose some guidelines for future assessment research with ethnic minorities to improve the knowledge base not only for ethnic minorities but also for the field of psychological assessment. In doing so, we will closely examine fundamental problems such as sample heterogeneity, measurement of culture, and underlying assumptions about ethnicity, all of which make assessment research with ethnic minorities inherently challenging. Because our work involves Asian Americans, many of the cited examples deal with this population, although the point behind the examples may apply to other ethnic groups. We refer to assessment research in a broad sense and use examples from extant literature on cognitive, personality, and clinical psychodiagnostic assessment with various ethnic mi