The World Health Organization’s (WHO) global public health mandate includes a focus on expanding access to HIV testing, antiretroviral therapy (ART) and treatment monitoring to improve the clinical management of HIV, achieve sustained viral suppression, and prevent HIV-related incidence, morbidity, and mortality. This article documents key moments in research and WHO policies that have informed how ART is applied within HIV programs, including as a prevention tool with the potential to support efforts to address HIV-related discrimination. For more than 20 years, WHO has promoted the benefits of HIV treatment including as part of the approach to prevent the mother-to-child transmission (vertical transmission) of HIV. WHO guidance has followed, and continues to follow, the evolving evidence. In 2023, WHO continues to clarify that there is zero risk of sexual HIV transmission when a person living with HIV has an undetectable viral load and an almost zero or negligible risk of sexual transmission when a person living with HIV has a viral load of ≤1000 copies/mL – helping to evolve the focus of community campaigns and health worker training to include a focus on ‘virally suppressed’ while also continuing to emphasise the ultimate goal of achieving an undetectable viral load. This evolution does two things: first, it strongly reasserts the evidence around there being no chance of transmission if a person has an undetectable viral load; and second, it provides an extremely strong degree of confidence that, similarly, individuals who are virally suppressed will not pass on the virus sexually. WHO is now encouraging positive and clear messaging to highlight that the consistent use of ART prevents onwards HIV transmission.