Nearly two decades of research have demonstrated the benefit of public health programs to prevent the spread of HIV/AIDS among high risk groups. Those that help sex workers protect their health and human rights are among the prevention strategies designated "best practices" by UNAIDS and the World Health Organization (WHO). These efforts have shown success in containing an epidemic that has already claimed 23 million lives. Markedly scaling up such programs can reduce by half the estimated that are otherwise expected to occur within the decade.