PROJECT SUMMARY/ABSTRACT The goal of this training grant is to equip junior investigators with the skills to make enduring contributions to child digestive health, which encompasses processes that are critical for the survival, growth, and well-being of people and populations. We achieve this goal by providing immersive research training at Washington University in fields relevant to digestive health of children worldwide. The rationale for our training program is based on two premises: (1) high quality early career training is critical for producing individuals who will make meaningful and lasting impact on the field, and (2) too few individuals are adequately trained to solve problems relevant to the childhood digestive system. Mentors across all disciplines share dedication to research relevant to digestive health of children, have strong training records, are very well supported by federal and foundation grants, and integrate our T32 trainees into existing projects to prepare them for productive scholarly careers. Track I (Microbial–Host interactions in the Gastrointestinal Tract) trainees determine how gut pathogens and microbial populations beneficially or harmfully affect childhood digestive health. Track II (Cellular and Molecular Biology of the Developing Gastrointestinal Tract) trainees dissect molecular and genetic aspects of congenital and acquired disorders of the childhood gastrointestinal system and host response to inflammatory stimuli. Track III (Translational Biology of the Gastrointestinal Tract) trainees use data from humans and populations to further knowledge of digestive disorders of childhood. This program will fund four post-doctoral (MD, PhD, or MD-PhD) drawn from our traditional base of pediatric gastroenterology fellows and post-doctoral trainees, strengthened in the past five years by extension to surgical residents. We will also fund members of the expanding community of PhD and MSTP students interested in the problems we strive to solve by also funding pre-doctoral candidates and Medical Scientist Training Program enrollees. Applicants to the program will receive two years of highly mentored support, including an external mentor system. We will also expand our portfolio of training opportunities to include large data base analysis, nationwide cohort study training, and implementation science. We will also co-sponsor an annual retreat focused on issues of diversity, equity, and inclusivity in our training, research, and clinical care. The program will also remain integrated into the Washington University Digestive Diseases Research Core Center (DDRCC). The trainees we fund also strengthen multilevel collaborations between gastroenterology and surgical research in our institution. Our intent is to produce scientists with enduring interests in childhood digestive diseases and their causes, treatments, and prevention, by our cohorts of trainees and mentors who share complementary goals and skills.