NIDA's Cooperative Agreement program to reach out-of-treatment drug users and provide HIV prevention to reduce HIV drug and sexual risks was initiated in September of 1990. By August, 1994 the program included 23 sites which used various theoretical models to guide prevention strategies, add conceptual coherence to many aspects of behavior change, and allow for clearer interpretation of why behavior change occurs. This article reviews the theoretical models used at each of the NIDA Cooperative Agreement sites, the perceived helpfulness of the models, and recommendations for future initiatives.