This paper explores the connections between ethnicity and sexuality. Racial, ethnic, and national boundaries are also sexual boundaries. The borderlands dividing racial, ethnic, and national identities and communities constitute ethnosexual frontiers, erotic intersections that are heavily patrolled, policed, and protected, yet regularly are penetrated by individuals forging sexual links with ethnic "others." Normative heterosexuality is a central component of racial, ethnic, and nationalist ideologies; both adherence to and deviation from approved sexual identities and behaviors define and reinforce racial, ethnic, and nationalist regimes. To illustrate the ethnicity/sexuality nexus and to show the utility of revealing this intimate bond for understanding ethnic relations, I review constructionist models of ethnicity and sexuality in the social sciences and humanities, and I discuss ethnosexual boundary processes in several historical and contemporary settings: the sexual policing of nationalism, sexual aspects of US-American Indian relations, and the sexualization of the black-white color line.