The AIDS epidemic is one of the greatest development challenges of the 20th century. Since 1986, the World Bank has supported member countries' efforts to fight the epidemic in many ways including committing over US$550 million to HIV/AIDS prevention and mitigation efforts. This paper, the first comprehensive study of all World Bank HIV/AIDS-related activities, assesses the appropriateness of Bank interventions from the perspective of public economies and reviews the economic evaluation and implementation of projects.