Modified Project Summary/Abstract Section PROJECT SUMMARY/ABSTRACT CORE K: SUBSTANCE USE RESEARCH CORE Substance use is a key risk factor for HIV transmission and a leading driver of morbidity and mortality among people with HIV (PWH). The Ending the HIV Epidemic (EHE) strategies and U.S. Office of AIDS Research priorities of reducing comorbidities in PWH can only be achieved if clinical and public health approaches effectively address the widespread impact of substance use and its causes. To meet these crucial needs, the Substance Use Research Core (SURC) will support clinical, behavioral, translational, and basic science substance use and HIV (SU/HIV) research by offering services to CFAR investigators at each stage of a research project. The SURC will advance SU/HIV collaborations within and across CFARs and foster a robust research workforce. Accordingly, the SURC will pursue the following Specific Aims: 1) To provide CFAR investigators expertise in developing research that addresses substance use as an impediment to EHE strategies and as a driver of HIV-associated comorbidities. The SURC will work with CFAR investigators to formulate innovative and scientifically sound SU/HIV research questions, including questions that address related syndemics and determinants of health; and will ensure that CFAR projects appropriately consider and incorporate the impact of substance use on HIV transmission, HIV viral suppression, and comorbidities among PWH. 2) To support CFAR investigators in conducting rigorous and innovative research that addresses crucial knowledge gaps around the impact of substance use on HIV outcomes. The SURC will advise and train investigators on methods for assessing substance use by conducting workshops and curating resources; support incorporation of effective and up to date substance use interventions; and assist with substance use intervention selection, interventionist training, fidelity assessment, intervention manual development, and adaptations. 3) To serve as a regional and national resource on SU/HIV research. The SURC will connect substance use investigators with HIV investigators to develop collaborative projects; convene topic groups across Providence/Boston CFAR and provide individual mentoring for SU/HIV researchers. Importantly, the SURC will serve as a national hub for collaborative SU/HIV research across CFARs, fostering exchange of ideas and enabling synergies through shared expertise and resources. The SURC will leverage our Inter-CFAR Substance Use Research Community, a nationwide SU/HIV research platform initiated and led by the SURC, to enhance research capacity across CFARs. The SURC will act as a regional and national catalyst to quicken the pace, depth, and impact of SU/HIV research and is uniquely positioned to support and prepare CFAR investigators to pursue research projects that cut across SU/HIV research and move us closer to ending the HIV epidemic, improving health outcomes for PWH, and addressi...