During the last twenty-five years we have learned how the human immunodeficiency virus (HIV) causes AIDS, how it spreads and how it does not. We have also watched as AIDS has destroyed whole populations, and observed which responses appear most efficacious. One of the most alarming characteristics of HIV is that it typically strikes healthy young people. Yet most of the people who have HIV still do not know it. Efforts to confront the epidemic are further stymied by contentious differences about how best do so, compounded by a persistent stigmatisation of and discrimination against people living with HIV/AIDS. There are some 4.1 million new cases every year, and though the recent rapid expansion of antiretroviral treatment will prolong the ...