Great advances have been made over the past decade in behavioral research on how to help persons avoid contracting HIV infections (primary prevention) and how to reduce or alleviate adverse consequences among persons who are living with HIV disease (secondary prevention). Within the primary prevention areas, research has shown the effectiveness of risk-reduction interventions undertaken with individuals, couples, small groups, communities, and at a social policy/structural level. Advances in HIV medical care have also created important new challenges and roles for behavioral scientists in the area of HIV secondary prevention. This article concludes by identifying key emerging issues in HIV behavioral research that will require attention in the years ahead.