The global epidemic of HIV in men who have sex with men (MSM) continues to expand in most countries, driven by high transmission probabilities through receptive anal intercourse and the ability of MSM to engage in both receptive and insertive anal sex. Molecular epidemiological data show substantial clustering of HIV infections in MSM networks, with higher rates of dual-variant and multiple-variant HIV infection compared to heterosexual populations. Prevention strategies that lower biological transmission and acquisition risks, such as antiretroviral treatments, offer promise for controlling the expanding epidemic in MSM. However, the hidden and stigmatized nature of MSM populations, along with structural factors such as lack of access to healthcare, continue to limit the effectiveness of interventions. The high transmission probability and the role of anal sex in MSM highlight the need for urgent reform in HIV programming, including combination approaches that address biological, behavioral, and structural risks.The global epidemic of HIV in men who have sex with men (MSM) continues to expand in most countries, driven by high transmission probabilities through receptive anal intercourse and the ability of MSM to engage in both receptive and insertive anal sex. Molecular epidemiological data show substantial clustering of HIV infections in MSM networks, with higher rates of dual-variant and multiple-variant HIV infection compared to heterosexual populations. Prevention strategies that lower biological transmission and acquisition risks, such as antiretroviral treatments, offer promise for controlling the expanding epidemic in MSM. However, the hidden and stigmatized nature of MSM populations, along with structural factors such as lack of access to healthcare, continue to limit the effectiveness of interventions. The high transmission probability and the role of anal sex in MSM highlight the need for urgent reform in HIV programming, including combination approaches that address biological, behavioral, and structural risks.