As the proportion of children with chronic conditions has increased exponentially over the last decades, there has been necessity for evolution of definitions, care models, and systems for their care. Chapter 2 discusses the further refinement of the definition of children with medical complexity and explores in depth the development of models of care for these children and how the workforce has started to meet the needs of this growing population. This chapter also touches on how these systems and models are beginning to integrate into the established pediatric frameworks of clinical care, financial reimbursement, and community supports. This includes discussion of shared decision making, coordination of care, and examples of integration between subspecialities, including palliative care. The burgeoning and critical subfield of transitional care to adulthood for children with medical complexity is also touched on.