We are proposing a partnership between the University of Washington (UW), and the University of Nairobi (UN) to work towards A Kenya Free of AIDS. This partnership draws on a 20 year history of the UW in building capacity for HIV/AIDS research at the UN, and the strength of the population science community at both institutions and in other institutions in the Nairobi area. The program will support several ongoing research collaborations between scientists at UW and the University of Nairobi that are well positioned to benefit from the contributions of social science. Each of these projects focuses on HIV prevention. Our specific aims are: 1. To build capacity for rigorous social and behavioral science research on HIV/AIDS through a combination of (a) Research infrastructure support, (b) Faculty development, (c) Mechanisms for building an interdisciplinary scholarly community, and (d) Enhancing IRB training and procedures at the University of Nairobi; and 2. To conduct foundational interdisciplinary research projects in HIV prevention focused on (a) A widow inheritance intervention, (b) A prevention of mother to child transmission (PMTCT) intervention, (c) Translation of a secondary transmission prevention intervention, and (d) A life course study of female sex workers and their male clients. The UW brings strong institutional resources to this partnership, with an active Sociobehavioral and Prevention Research core in the Center for AIDS Research (CFAR), and a group of population scientists with interests in HIV in the Center for Studies in Demography and Ecology (CSDE). The University of Nairobi has a parallel set of units, with a new University Centre for HIV Prevention and Research (UCHIVPR) and well established Population Studies Research Institute (PSRI). In both institutions, this grant will help to establish the mechanisms to promote the interaction between social science, public health and biomedical research. Nairobi is also home to the African Population Health Research Center, and the Population Council. Both have agreed to work together with us on this initiative. As behavior changes are beginning to make progress in prevention, new biomedical prevention interventions are coming online. Increasingly, it is recognized that the biomedical and behavioral prevention efforts must work together for HIV prevention and treatment efforts to succeed. This application will provide a mechanism to facilitate the cross-disciplinary research needed to develop the next generation of integrated HIV/AIDS prevention strategies.