Every year UNAIDS provides revised global, regional and countryspecific modelled estimates using the best available epidemiological and programmatic data to track the HIV epidemic. Modelled estimates are required because it is not possible to count the exact number of people living with HIV, people who are newly infected with HIV, or people who have died from AIDS-related causes in any country. Doing so would require regularly testing every person for HIV and investigating all deaths, which is logistically infeasible and ethically problematic. Modelled estimates—and the lower and upper bounds around these estimates—provide a rigorous representation of the HIV pandemic in terms of levels and trends. Related links: New UNAIDS report shows AIDS pandemic can be ended by 2030, but only if leaders boost resources and protect human rights now | Full report