Genetic research aimed at understanding human health and disease is grounded in the study of genetic variation. The inclusion of research subjects with diverse ancestral backgrounds is essential for genetic and genomic research that fully explores human diversity. Large-scale cohort studies and biobanks in Europe and the United States often do not include the breadth of ethnic and racial diversity observed in their countries' citizens. This article explores the findings of a qualitative study of U.S. scientists' understanding and views of the NIH Policy and Guidelines on the Inclusion of Minorities as Subjects in Clinical Research. The findings suggest that the policy restricts how scientists use racial and ethnic categories to define and report their study populations and does little to motivate their efforts to increase the inclusion of non-European ancestral populations in genetic and genomic research.