ABSTRACT The physician-scientist workforce struggles to attract and maintain a pipeline of physician-scientist trainees. Physician-scientists, who hold dual expertise in clinical medicine and research, are uniquely skilled in addressing the challenges in health, disease, and health care, but there is a well-recognized shortage of these professionals. One population that has not received sufficient attention with regard to professional development as physician-scientist is that of undergraduate medical students. Prior work has demonstrated that research career intentions evolve significantly during medical school and that research career intentions at graduation are associated with tangible downstream measures of research success, including subsequent receipt of NIH funding. However, little is known about the individual and institution-level factors and experiences that foster professional development as physician-scientist during medical school, particularly among MD program students, who make up the vast majority of medical students in the U.S. We propose a 5-year, longitudinal study to identify trajectories (i.e., evolution over time) of research career intentions, and determinants thereof, in 600 students matriculating into U.S. MD programs. We will examine experiences at the individual level, such as quality of mentorship and research experiences, as well as experiences at the institutional level, such as education about the physician-scientist pathway and opportunities for doing research, and their impact on research career intentions during medical school. The aims are to: 1) identify trajectories of research career intentions among students throughout medical school training, from matriculation to graduation and 2) identify student- and institutional-level predictors of research career intention trajectories. This study is significant because it will identify potentially influential timepoints and predictors of change in research career intention among MD students that can be used to strengthen the physician-scientist workforce pipeline during the formative years of medical school. The impact of our findings will be enhanced by our strong partnerships with national organizations, including medical education leaders at the National Academies of Sciences, Engineering, and Medicine (NASEM) and Association of American Medical Colleges (AAMC) to disseminate our findings. This study will form the basis of a future proposal to conduct follow-up of the cohort assembled in this study through residency and into early- and mid-career positions to further disentangle the process of professional identity formation as physician-scientist among U.S. medical trainees.