Budgetary issues have intensified the focus on improving efficiency in publicly funded health programs. Yet Medicare and Medicaid insure some of the most ill or disabled patients, who are also some of the most expensive. Proposals to address costs create incentives to increase care coordination and accountability for the continuum of care. Realizing spending reductions in this population, however, needs to be balanced with assuring quality for a group at high risk for mortality, functional loss, and decline in quality of life. The overarching goal of this project is to study how fragmentation of care, and the reverse, increased integration, vary with cost and quality of care for high need beneficiaries, including patients dually eligible for Medicare and Medicaid. Efficient care for high need patients may require a broad network that includes multiple physician specialties, acute care hospital, and other types of inpatient care (psychiatric, long term acute hospital or nursing home). In previous work, we have developed an actionable unit - the physician-hospital network - which links Medicare beneficiaries to the specific physicians and hospitals that deliver the majority of their care. We seek to broaden this approach with respect to high need patients using observational cohort methods. We will use national Medicare, Medicaid and Minimum Data Set data to address major gaps in the literature. In Aim 1, we will define networks of healthcare providers for high need patients, and how patients, care, and spending are distributed within and across these networks. In Aim 2, we will test how cost and quality of care for high need patients vary with system (i.e. provider network and region) characteristics. And in Aim 3, we will take advantage of changes in the marketplace to study how cost and quality measures change as health systems formally integrate. The long-term impact of this work will be to provide rigorous information about who can reasonably be held accountable for the care of high need patients and identify the points of leverage for improving outcomes.