PROJECT SUMMARY/ABSTRACT Dr. Pulcini proposes a five-year research training program to support his development into an independent physician-scientist dedicated to improving emergency care of children with medical complexity, which account for approximately 20% of all pediatric emergency department (ED) visits and 33% of all healthcare spending among children. Dr. Pulcini’s project goal is to optimize and implement a user-centered emergency care planning tool to improve outcomes for infants with medical complexity (notably those in rural areas), a particularly vulnerable subset of this patient population. Under the first aim of the proposal, Dr. Pulcini will optimize an existing emergency care planning tool that, despite advocacy for children with medical complexity by two professional societies, has been poorly implemented to date. Dr. Pulcini will optimize the emergency care planning tool for infants with medical complexity through iterative semi-structured and targeted interviews and surveys of tool users: providers, local interdisciplinary collaborators, and families. Under the second aim, Dr. Pulcini will design and conduct a randomized feasibility trial of the user-centered emergency care planning tool’s implementation, measuring resultant emergency health care outcomes. As part of the trial implementation process, Dr. Pulcini will monitor barriers to implementation, as well as measure key emergency health service research measures with plans for cost-effectiveness analysis for a full-scale future randomized controlled trial to be submitted as an R01. Dr. Pulcini’s training program is focused on dissemination and implementation (D&I) science, supplemented with training in clinical trials and health services measure development. The training in D&I science builds upon Dr. Pulcini’s previous training in pediatric emergency medicine and maternal and child health. Dr. Pulcini’s research will be supported by an accomplished group of mentors with expertise in D&I science, clinical trials, pediatric emergency medicine and health services research. His mentors are dedicated to ensuring his career development into an independent clinical investigator through successful conduct of the proposed project and training plan. By providing Dr. Pulcini with the skills and mentored experience necessary to complete this proposal, he will be well positioned to succeed as an independent scientist and significantly improve the emergency care of children with medical complexity.