Using applied behavioral science techniques that have been successful in other areas of health promotion, community-level campaigns were implemented in 5 cities to prevent HIV infection among hard-to-reach, at-risk populations: men who have sex with men but do not self-identify as gay; women who engage in sex for money or drugs; injecting drug users (IDUs), female sex partners of IDUs; and youth in high-risk situations. Communication materials presented positive role models for risk-reducing behaviors, and peer networks prompted and reinforced the behavior change process. This article describes the first year of intervention experience and documents the practical application of theoretical concepts of persuasion and learning. The use of theory and data to develop 188 educational messages is illustrated and training methods and experiences are reported for 150 peer leaders, 104 other community networkers, and 22 outreach workers. These activities are feasible and appear to offer an effective, general approach for diverse, special populations.