The global diversity of HIV epidemics can be explained in part by types and patterns of sexual partnerships. We offer a typology of sexual partnerships that corresponds to varying levels of HIV-transmission risk to help guide thinking about appropriate behavioral interventions, particularly in the epidemics of sub-Saharan Africa. Declines in HIV prevalence have been associated with reductions in numbers of sex partners, whereas many other prevention strategies have not been demonstrated to reduce HIV transmission at a population level. We suggest a reorientation of current prevention efforts, based on the epidemiology of sexually transmitted HIV epidemics and trends in sexual behavior change. Concurrent sexual partnerships are likely to play a large role in transmission dynamics in the generalized epidemics of East and Southern Africa, and should be addressed through improved behavior-change interventions.