The contexts in which the human immunodeficiency virus (HIV) pandemic is occurring are increasingly diverse. Individual-level risks for HIV infection are at the core of these epidemics and are powerfully impacted by social, structural, and population-level risks and protections. The emerging epidemics among injection drug users across Eurasia are largely the result of needle sharing, but the drivers of disease spread include increases in opiate availability, limited HIV infection prevention and programs for drug users, and undermining policy environments. An emerging epidemic of HIV infection among men who have sex with men in developing countries is primarily spread through unprotected anal intercourse but is also driven by limited HIV infection prevention services, social stigma, and the lack of human rights protection. The epidemic in southern Africa, which is spreading largely through heterosexual exposure, is driven by high rates of labor migration, concurrent sexual partnerships, gender inequalities, and the limited availability of male condoms. We need to do much more to control HIV infection, and social and structural risks are crucial intervention targets.