Community interventions and interventions targeting specific groups at risk of STDs/HIV have demonstrated significant impacts on sexual behavior, particularly condom use and safer sex. The scientific evidence suggests the factors that make these interventions particularly effective include the establishment of community, including business and CBO partnerships; maintainance of the intervention post-research funding; and buy-in by the community or target group. The modification of risky normative beliefs through the use of opinion leaders and role models, and through intervention delivery by peer educators, is an important facet of such interventions. Interventions delivered by health professionals, absent a community base, appear to be unsuccessful. Where cultures or subcultures are targeted, the close involvement of such groups in the design and delivery of messages is critical to their success. Diffusion of interventions through existing social networks further extends the intervention into the community and acts to reinforce and maintain changes in peer norms toward safer sexual behavior. The available data confirm that community or medical infrastructure-based interventions are effective in changing sexual behavior and can reach a wider range of the population than face-to-face programs if they incorporate peer educators as role models in modifying norms, and if diffusion of the intervention is integral to the design.