This article argues for a more systematic inclusion of human sexuality in studies of ethnicity and nationalism. Reviewing key extant social science research on sexuality, it highlights how scholars can leverage its theories, methods, and findings to enhance our understanding of the ways people build imagined ethnic and national communities and draw symbolic boundaries around them. This research reveals that sexuality is not tangential to those activities. Rather, policymakers, religious institutions, local communities, families, and other organizations all participate in more or less obvious ways to define what kinds of sexual desires, behaviours, and identities are acceptable for legitimate citizenship and group belonging. Those decisions have ramifications on both the global scale of international relations and the local scale of personal self-understanding. For these reasons, this article argues that scholarship that elides sexuality may run the risk of painting an incomplete picture of social processes related to ethnicity and nationalism.