PROJECT SUMMARY The expansion of Medicaid coverage after the passage of the Affordable Care Act (ACA) has increased Medicaid coverage to 15% of the working-age adult population. Nationwide, 77% of Medicaid enrollees are in Medicaid Managed Care (?Medicaid MC?) plans. To constrain costs, Medicaid MC plans often contract with smaller sets of included physicians and hospitals (?networks?) than other insurance types. These smaller networks (?narrow networks?) have been quantified for ACA Marketplace plans and shown to be associated with reductions in patient access to care. A possible byproduct of smaller physician networks may be that physicians included in these narrow networks are more tightly connected, which could potentially result in more coordinated care for Medicaid MC enrollees. However, to our knowledge, no empirical research has examined the association between narrow networks and care coordination. Better understanding the association between narrow networks, quality, and coordination for Medicaid MC enrollees is critical to ensure continued access to high quality care for this vulnerable low-income population. Using state all payer claims databases (APCD) of commercial insurance and Medicaid claims from Massachusetts, New Hampshire, Colorado, Utah, and Oregon for 2014-2015, we will measure how narrow Medicaid MC physician and hospital networks are and examine their association with the quality and coordination of care received by Medicaid MC enrollees compared to Medicaid FFS and commercially insured enrollees. The goal of this research is to conduct a timely analysis of the current Medicaid MC market to provide information for future health insurance regulations regarding provider networks, particularly those used by low-income and vulnerable populations. Disparities in access for low-income and minority populations are well documented, with lower access to providers; we will measure whether this arises in part from differences in provider networks, which would suggest future policy clarifying and enforcing network adequacy standards may be an effective policy lever to improve access, quality, and coordination for Medicaid MC enrollees. This is a low cost, high impact secondary data analysis study by a well-qualified team of investigators. It will provide essential information on the relationship between narrow networks, quality, and coordination; the results will be used as a basis for future studies designed to examine the formation of these networks across insurance markets and to optimize the size and composition of these networks.