BIO-BEHAVIORAL CORE PROJECT SUMMARY The Bio-Behavioral Core represents an innovative programmatic approach for the UCSF-Bay Area Center for AIDS Research (CFAR). During our strategic planning process with research, clinical, policy, and community stakeholders, we identified three critical ways in which our CFAR needed to expand to meet the needs of investigators and be responsive to NIH HIV-focused research priorities. These three expansions are in the areas of HIV prevention, substance use research, and assessing biomarkers of behavior, such as objective metrics for adherence and substance use. First, we now support a diverse cohort of persons on PrEP housed at our San Francisco Department of Public Health (SFDPH) affiliate, which provides infrastructure for a range of research inquiries (PrEP Cohort). The PrEP cohort collects survey data and specimens on participants on PrEP (oral and injectable when available) and is nimble for add-on studies from early-stage investigators (ESIs). Second, we will provide expert consultation on integrating measurement and intervention approaches that are responsive to significant challenges of substance use in HIV prevention and treatment (Substance Use Research Program). Harnessing expertise at UCSF and our affiliates, this new Program will address one of the greatest challenges in HIV prevention and care to try to optimize outcomes. Third, the Bio-Behavioral Core supports the development, implementation, and analysis of biomarkers of behavior, specifically objective metrics of adherence and substance use in HIV research (Biomarkers of Behavior Program). This new program will provide assays and interpretation of these metrics to support the PrEP cohort and the Substance Use Research Program. The new Bio-Behavioral Core will work closely with the other Cores and working/interest groups to ensure efficient use of CFAR resources to address overall Center aims and crosscutting priorities of health equity/community engagement, international HIV research, and training/career development. The PrEP cohort uses the same data elements and infrastructure as the SCOPE cohort in the Clinical Core; the Bio-Behavioral Core components will all support ESIs and investigators from underrepresented minority (URM) backgrounds in the Developmental Core; and this Core will work closely with the new Housing and Intersectionality Scientific Working Groups (SWGs) on structural determinants of health. Collectively, this new Core will provide added value by addressing previous gaps in the capacity of CFAR investigators to meet emerging challenges of the HIV epidemic, provide a platform for ESIs to build programs of research, and enable investigators to conduct community-engaged work aimed at mitigating HIV and related health disparities.