Criminalization of HIV transmission and exposure is an ineffective tool for combating AIDS and a costly distraction from programs that we know work--programs such as effective prevention, protection against discrimination, reducing stigma, empowering women and providing access to testing and treatment. In this article, which is based on a public lecture he gave at "From Evidence and Principle to Policy and Action," the 1st Annual Symposium on HIV, Law and Human Rights, held on 12-13 June 2009 in Toronto, Canada, Justice Edwin Cameron analyzes the surge in criminal prosecutions, discusses the role that stigma plays in these prosecutions and makes the case against criminalization.