This technical bulletin gives an overview to what treatment as prevention (TasP). Treatment as prevention (TasP) is a HIV prevention intervention where treating an HIV-positive person with antiretroviral medication is used to reduce the risk of transmission of the virus to a negative partner. The primary purpose of antiretroviral treatment (ART) is to treat HIV disease in order to improve health and extend lifespan. TasP is a secondary benefit of ART. The bulletin highlights the challenges and risks to MSM using the TasP method and details the current research for the TasP method globally.