This chapter reviews scientific studies of the risk of HIV and other sexually transmitted infections among male sex workers. It reports on sexual risk behavior as well as psychosocial and structural factors that contribute to the spread of HIV. It also discusses access to HIV prevention and treatment, along with biomedical and behavioral interventions intended to reduce HIV acquisition and transmission. In addition, the authors address the human rights implications of these studies and highlight new areas in need of research and exploration. The authors emphasize that there are many types of male sex workers, including Internet escorts, street workers, masseurs, and dancers, and each may have different sexual risk behaviors. Male sex workers who solicit clients on the Internet, for example, may have a different risk profile than those whose work is street based. Similarly, conditions for individuals whose primary source of income is sex work may differ significantly from men who engage in sex work infrequently. Given this population’s heterogeneity, health and governmental officials must generate and implement innovative treatment and prevention approaches tailored to their specific needs. These interventions should be integrated with biomedical approaches that address complex psychosocial factors and risk-taking behaviors. In addressing sexual health disparities among male sex workers, it is essential to concentrate on key structural factors, including the decriminalization of sex work, the reduction of sex work–related stigma and discrimination, and increased access to services that focus on mental health, sexual health, and substance abuse. Male sex workers should be included in planning and developmental efforts aimed at improving access to and participation in HIV treatment and prevention. Ultimately, committed advocacy, funding, surveillance, programmatic efforts, and research are all central both to public health and to the achievement of social justice.