Medically complex children refer to patients who need intense medical care due to multisystem dysfunction, technology dependence, or complex medication needs. Medically complex patients often consume largely disproportionate amount of different care resources in hospitals. Understanding the nature of complexity and predicting the dynamics of complexity in patients can help design better personalized care plans in order to improve quality and reduce cost. Due to the heterogeneity in the complexity, we still do not have precise definitions of medically complex patients (MCP), nor the understanding of different MCP phenotypes. Finally, in order to directly impact care process, we also need predictive scores for each MCP phenotypes so that we can identify the high-risk patients earlier.