Persons with continuous complex care needs frequently require care in multiple settings. During transitions between settings, this population is particularly vulnerable to experiencing poor care quality and problems of care fragmentation. Despite how common these transitions have become, the challenges of improving care transitions have received little attention from policy makers, clinicians, and quality improvement entities. This article begins with a definition of transitional care and then discusses the nature of the problem, its prevalence, manifestations of poorly executed transitions, and potentially remediable barriers. Necessary elements for effective transitions are then presented, followed by promising new directions for quality improvement at the level of the delivery system, information technology, and national health policy. The article concludes with a proposed research agenda designed to advance the science of high-quality transitional care.