My dissertation will explore the ways that the U.S. and Mexico, through immigration laws, medical regulation, and deportation, shaped the twentieth-century U.S.-Mexico border into a site of (homo)sexual policing and exclusion. Historians and other scholars have recently studied the ways that constructions of sexuality—including sex work, homosexuality, and sex-related diseases— have influenced immigration experiences and state control over immigration. However, this scholarship has largely been constrained to a nation-state analysis that forecloses a transnational, borderlands framework for analyzing immigration and sexuality. It has also tended to focus on discrete forms of sexuality. Building on discoveries made in archives, my dissertation examines how policing actually brings together diverse sexualities—from prostitution to the hyper-medicalization of venereal disease to homosexuality. Further, I examine how these forms of policing developed in relationship to one another transnationally, a cross-pollination of policing methods that allowed each state to hone its sexual surveillance and disciplining power across the border. Sexual policing in this context functioned as a regional and coordinated project between nation-states that marked sexuality as a central element of identity controlling mobility, citizenship, and assimilability.