The history of government action on HIV/AIDS has much to teach us about the dynamics and possibilities of US public health policy, but it has been insufficiently studied by social scientists of the epidemic. This article draws on a large set of original interviews with policy makers, thousands of news articles, and extensive documentation to reconstruct the history of three areas of debate and decision making about HIV prevention since 1990: needle exchange, HIV testing, and sex education for at-risk groups. These histories illuminate three key lessons. First, scientific evidence has less power to drive public health policy in the United States than in the United Kingdom, which is used as a comparison case to contextualize US choices within a broader range of options. Second, moral concerns weigh so heavily in the United States that a publicly articulated moral argument can countermand the dictates of solid scientific evidence, the voices of experts, and practical considerations to push public health policy in entirely oppositional directions. Third, having the ear of the presidential administration is usually a necessary—although not always sufficient—condition for the success of advocates trying to move US policy in the public health-indicated direction.