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 three joint doctoral programs in public health, clinical psychology and a new PhD in 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. Our objectives are: 1) To provide opportunities for interdisciplinary research training experiences for pre-doctoral students and postdoctoral fellows in epidemiology, health behavior and psychology who wish to focus on prevention research at the intersection of substance use and HIV or other infectious diseases (e.g. viral hepatitis, TB, STIs) or comorbidities; 2) To offer students hands-on experience in the study of HIV and related comorbidities in international settings which bear the greatest burden of injection drug use, HIV and related infections; 3) To recruit and train researchers from diverse academic backgrounds and under-represented minority populations (URM) with the tools needed to become independent researchers with state-of-the-art skills to address high priority challenges in HIV prevention research among substance users; and 4) To train individuals in the responsible conduct of research with human subjects, especially in international and cross- cultural settings. During the past 4 years, our program supported 31 trainees (12 predoctoral and 19 postdoctoral fellows; 12 (39%) were URM). Of completed trainees (8 predocs and 16 postdocs), all but 1 predoc and 1 postdoc are still active in the field. Time to matriculation for predocs averaged 4.1 years. Three completed predocs are Assistant Professors, 2 are postdocs funded by other NIDA T32s, and two are in applied positions that include research. Seven K01s were newly awarded to postdocs with 3 more pending NGAs; half of these were URM. Our 31 predocs and postdocs published 82 and 141 manuscripts, respectively, almost half of which were first authored. We request support for 4 predoctoral and 4 postdoctoral trainees, who will be mentored from a pool of 25 Preceptors. Depending on their level of training, mentees complete courses in substance use and infectious diseases, instruction in responsible conduct of research, quarterly cultural sensitivity training workshops, seminars on scientific rigor, presentations on 'Work In Progress', and new seminars (e.g., Writing Circle). Our active research projects in nearby Mexico (6 R01s) and several other international settings offer the opportunity for unique, hands-on international training experiences and a robust infrastructure for trainees to develop into independent investigators.