PROJECT SUMMARY Immersed in the two worlds of clinical practice and research, physician-scientists, particularly those trained in quantitative social sciences, have unique perspectives that are key to effectively addressing the healthcare demands of America?s aging population. Harvard University, home to a long established nationally recognized MD-PhD program as well as world-renowned graduate programs in Health Policy, Economics, and Social and Behavioral Sciences, is exceptionally well poised to train physician-scientists in these areas. With the support of this institutional NIA training grant, we have cultivated a growing cohort of such trainees and are inspiring them to pursue impactful aging related research. Training typically follows a ?2-4-2? model: 2 years of medical school, 4 years of graduate school culminating in a PhD with at least one project focused on aging populations, and then, 2 final years of medical school. While the accent is aligned with their tuition assignment, students participate in clinical and research training throughout their timeline. Hallmarks of this training program include regular tutorials run as well as meetings with the directors of the Marcus Research Institute of Aging. Both opportunities provide students with mentorship, community, interdisciplinary interactions, exposures to a wide range of social science quantitative methods, and provide a forum for identifying exciting research questions. Students are appointed to this training grant in the M1, M2, G1, M3 and M4 years. The G2-Gn years are covered by their respective PhD program. Our participating PhD programs include 1) the PhD Program in Health Policy (concentrations in Economics, Management, and Methods for Policy Research), which trains students for research and teaching careers in health policy through an interdisciplinary and interfaculty approach; 2) the PhD Program in Economics in the Department of Economics, which prepares students for productive and stimulating careers as economists in academia or for positions in government, research organizations, or business enterprises; and, 3) the PhD in Population Health Sciences (field of study in Social and Behavioral Sciences), offered through the Harvard TH Chan School of Public Health, which prepares students to be scholars whose research illuminates social and behavioral determinants of health and develops and evaluates innovative interventions and policies leading to the improvement of population health. The 28 participating faculty by and large possess a strong interest in and experience with mentoring physician-scientist trainees and have expertise in aging-related research. Within the greater community of ~190 MD-PhD students and ~27 social science MD-PhD students is now a vibrant and tight knit group of 10 who are part of this NIA training program. With an existing track record of distinguished alumni and this growing cohort of current trainees, made possible by this NIA training grant, we submit this competing renewal so that we may continue to build on these accomplishments.