PROJECT SUMMARY/ABSTRACT Adolescence presents an ideal developmental transition period for an integrated intervention targeting prevention of HIV risk behaviors and intimate partner violence (IPV), including sexual violence. Adolescent boys in particular are at high risk for HIV and perpetration of IPV. Yet, few behavioral interventions integrate HIV-IPV prevention and are tailored for the unique developmental needs of adolescent boys. In this study, we build on previous scientific work that demonstrated the acceptability and feasibility of Safe South Africa, an integrated HIV-IPV intervention that uses a developmentally- and gender-tailored approach grounded in social norms theory to prevent adolescent HIV risk behavior and IPV. We work in South Africa, a country with the largest HIV epidemic and some of the highest rates of IPV in the world. We propose the following specific aims: (1) Tailoring Safe South Africa intervention content to address the unique behavioral and social norms data that drives HIV and IPV behaviors among boys in their socioecological environments. (2) Testing the efficacy of the Safe South Africa intervention in preventing HIV/STIs and reducing IPV frequency among N=836 adolescent boys (ages 15- 17), with our working hypothesis that the intervention, relative to the usual care condition, will show (a) lower incidence of any STI (including HIV); and (b) reductions in IPV perpetration frequency and decreased endorsement of IPV supportive attitudes. (3) Identifying barriers and facilitators to implementing Safe South Africa within a school setting to provide data for future dissemination (presuming Safe South Africa is efficacious). We examine processes critical to future dissemination through (a) fidelity data examining adherence to core active components of the standardized intervention manual guiding consistent delivery of the intervention; and (b) qualitative data on the experience during and post-implementation from adolescents and stakeholders using N=20 in-depth interviews.