The AIDS epidemic update reports on the latest developments in the global AIDS epidemic and has been published annually since 1998. The 2007 edition provides the most recent estimates of the epidemic's scope and human toll and explores new trends in the epidemic's evolution. This is a joint UNAIDS and WHO report and the estimates produced by the UNAIDS/WHO Working Group on Global HIV/AIDS and STI Surveillance are based on methods and parameters that are informed by the UNAIDS Reference Group and HIV/AIDS Estimates, Modelling and Projections. These estimates are also based on work by country analysts in a series of 11 regional HIV estimates workshops conducted in 2007 by UNAIDS and WHO. The process and methodology used by UNAIDS and WHO were reviewed and endorsed by an International Consultation on AIDS Epidemiological Estimates convened jointly by the UNAIDS Secretariat and WHO on 14-15 November 2007 in Geneva.