This application requests support for a training program that prepares highly qualified pediatricians to assume leadership positions as investigators in Pediatric Infectious Diseases. Based in the Division of Infectious Diseases at Boston Children’s Hospital, the program takes advantage of the rich academic and research resources of Harvard Medical School, Harvard T.H. Chan School of Public Health, and affiliated teaching hospitals to bring together outstanding didactic experiences and research opportunities relevant to infectious diseases of children. Support for three positions per year is requested. Pediatricians enter the program for a minimum of three years of integrated clinical and research training that includes at least two years of supervised research under the mentorship of a member of the teaching faculty. The 31 members of the teaching faculty are accomplished investigators and experienced mentors chosen from the Division of Infectious Diseases at Boston Children’s Hospital and affiliated units at other Harvard institutions. Under the guidance of the research mentor and the Program Steering Committee, an individualized curriculum is designed for each trainee in one of three broad areas of investigation: microbial pathogenesis, host response and vaccines, or epidemiology and health outcomes. Trainees in the epidemiology and health outcomes pathway have the opportunity to earn a Master of Public Health degree from the Harvard School of Public Health as an integral part of the training program, providing training in epidemiology, biostatistics, clinical trial design, and analytical methods. Additional specialized training in infection control, antimicrobial stewardship, or transplant infectious diseases is also offered. All trainees have seminars and tutorials in grant preparation and scientific writing that supplement the mentored research experience. An individual Scholarship Oversight Committee is appointed for each trainee to monitor progress and to provide career guidance. During the second or third year, trainees are expected to present their work at national meetings, to prepare one or more manuscripts for publication, and, in most cases, to apply for a K08, K23, or other career development award to support the transition to independence as an investigator. Over the past ten years of the Pediatric Infectious Diseases fellowship program, 27 of 30 graduates have remained in academic positions, with 15 involved in research-based investigation, and 12 involved in primarily clinical academic activities.