Emergency medicine (EM) physicians practicing in the community are often the first providers to care for acutely ill children with medical complexity (CMC) as they arrive to their local emergency departments, which are often outside of major cities and may be in underserved areas. While many of these patients are ultimately transferred to tertiary care facilities at major medical centers such as theirs, EM physicians play a critical role in acutely stabilizing these patients prior to transfer or discharge home. This is despite often not having received specific education in this patient population during their training.  The purpose of this text is to provide an educational tool for physicians and other health care providers in the acute care of CMC. Comprised of clinical cases, it is a valuable resource for both early learners (e.g., pediatric residents, emergency medicine residents) as well as providers in practice who may see these patients regularly in the ED but did not receive extensive training on the care of CMC. Each chapter includes figures/tables/illustrations to aid in learning and ends with a summary in the form of 3-5 Take-Away Pearls.   Edited by three board-certified pediatric hospitalists,  Children with Medical Complexity in the Emergency Department  serves to help equip emergency medicine practitioners to provide optimal care for the most vulnerable and medically fragile patients in the communities they serve in order to enhance patient outcomes and provide a better experience for the patients' families. Chapter authors have been recruited from the pediatrics and emergency medicine fields, including generalists as well as subspecialty experts in the areas of transplant medicine, gastroenterology, nephrology, and many more.