Renewed funding is requested to continue a T32 training program to train the next generation of prevention scientists with expertise in HIV and related co-morbidities among substance users. Our program builds upon two joint doctoral programs in Public Health and Interdisciplinary Research on Substance Use offered in partnership between the University of California San Diego (UCSD) School of Medicine and the San Diego State University (SDSU) Graduate Schools of Public Health and Social Work, and a doctoral program in Biostatistics offered in the newly founded UCSD Herbert Wertheim School of Public Health. Our objectives are: 1) To provide interdisciplinary training experiences for pre-doctoral students and postdoctoral fellows in epidemiology, health behavior, and biostatistics, and public health who wish to focus on prevention research at the intersection between substance abuse and HIV or other syndemics (e.g. viral hepatitis, TB, STIs, SARS- CoV-2, overdose, stigma, trauma); 2) To support advanced training in key NIH research areas, including a new focus on data sciences applied to substance use and HIV or related syndemics in both domestic and international settings; 3) To recruit and equip researchers from diverse academic backgrounds and under- represented minority (URM) populations with the tools needed to become independent behavioral scientists with state-of-the-art skills in substance use and HIV prevention research; 4) To train individuals in the responsible conduct of research (RCR) with human subjects, especially in international and cross-cultural settings. In sum, during the past 4 years, our program supported 26 trainees (11 predoctoral and 15 postdoctoral fellows; 12 (46%) were URM). Of completed trainees 2017-2021, (8 predocs and 8 postdocs), all but 1 are still active in the field. Time to matriculation for predocs averaged 3 years. Five K-series awards were newly awarded to postdocs. Our 26 predocs and postdocs published 84 and 116 manuscripts, respectively, 44% of which were first authored. We request continued support for 4 predoctoral and 4 postdoctoral trainees, who will be mentored from a pool of 30 Preceptors. Depending on their level of training, mentees complete courses in substance use and infectious diseases, RCR instruction, quarterly cultural sensitivity training workshops, seminars on scientific rigor, presentations on 'Work In Progress', and seminars (e.g., Writing Circle). Our active research projects in nearby Mexico and numerous other lower and middle income countries offer the opportunity for unique, hands-on international training experiences and a robust infrastructure for trainees to develop into independent investigators focused on prevention of HIV and related syndemics among substance using populations.