The inclusion of minority racial/ethnic groups in biomedical research and clinical studies has taken on a new political significance in the last two decades. Against this background, my paper addresses a number of questions surrounding the in/exclusion of racial/ethnic minorities in biobanks designed for prospective epidemiological research into common, complex diseases. A number of commentators have been interested in questions of race/ethnicity in relation to biobanks, and this paper contributes to this debate by addressing three questions: whether, and in what ways, potential differences between ethnic groups figure in the creation, design, and rationale of biobanks, what scientific and social issues are involved in the inclusion and categorization of minority racial/ethnic groups in biobanks, and whether biobanks will help to ameliorate continuing health disparities experienced by minority groups. This paper begins to address these questions by considering in detail the case of one particular biobank—UK Biobank. This paper discusses interviews conducted with several key scientists working on UK Biobank that reveal how they conceived of the social, scientific, and practical issues of including these groups. I argue that the question of how and in what way racial/ethnic minorities would be included in UK Biobank—a project that has received substantial public funding—became a significant challenge that impacted on its final scientific design.