The role of migrants and mobile populations (MMPs) in the spread and control of HIV is increasingly being recognized and understood. While migration does not automatically equal HIV vulnerability, and not all MMPs are at increased risk of HIV as a result of their mobility, in many contexts MMPs are exposed to a unique set of sociocultural, economic, and environmental factors that render them more vulnerable to HIV including lack of access to health services, information, and environments that are conducive to engaging in high-risk behavior. Many of the underlying factors sustaining mobility including unequal distribution of resources, unemployment, socioeconomic instability, and political unrest are also determinants of increased risk of HIV. A rise in migration globally poses a unique set of challenges in ensuring access to HIV prevention, treatment, and care for mobile populations. Ongoing humanitarian emergencies continue to play a role in exacerbating the spread and impact of HIV.