Lesbians, prostitutes, women likely to have sex across racial lines, brought to the United States for immoral purposes, or arriving in a state of pregnancy -- national threats, one and all. Since the late nineteenth century, immigrant women's sexuality has been viewed as a threat to national security, to be contained through strict border-monitoring practices. By scrutinizing this policy, its origins, and its application, Eithne Luibheid shows how the U.S. border became a site not just for controlling female sexuality but also for contesting, constructing, and renegotiating sexual identity.Initially targeting Chinese women, immigration control based on sexuality rapidly expanded to encompass every woman who sought entry to the United States. The particular cases Luibheid examines -- efforts to differentiate Chinese prostitutes from wives, the 1920s exclusion of Japanese wives to reduce the Japanese-American birthrate, the deportation of a Mexican woman on charges of lesbianism, the role of rape in mediating women's border crossings today -- challenge conventional accounts that attribute exclusion solely to prejudice or lack of information. This innovative work clearly links sexuality-based immigration exclusion to a dominant nationalism premised on sexual, gender, racial, and class hierarchies.