Examining the Effects of Medicaid Managed Care Organizations' Entries and Exits for Medicaid Enrollees with Substance Use Disorders - Project summary Medicaid is an important source of health insurance for people with substance use disorder (SUD), currently covering approximately one in five adults with SUD. States have increasingly contracted with Managed Care Or- ganizations (MCOs) to administer services for their Medicaid population. They have also increasingly included, or carved in, behavioral health services into MCO plans. As a result of these trends, 31 states and Puerto Rico now enroll their Medicaid SUD population through MCOs. States determine, through a competitive procurement process, whether to renew or to end contracts with MCOs operating in their state, and whether to contract with new MCOs. Such MCO transitions may improve access and quality of care for Medicaid enrollees with SUD, but they may also lead to service disruptions that can negatively affect uptake and continuity of care for this vul- nerable population. Despite the importance of the MCO contracting process, little is known whether states are successful in removing low-performing MCOs and selecting high-performing MCOs through the procurement process, and what kind of state and MCO characteristics determine a successful procurement outcome. In this application, we propose a mixed-methods study to examine the effects of MCOs entries and exits as a result of the procurement process, and to explore factors at the state and MCO level that contribute to high- performing MCOs being selected to operate in a state and low-performing MCOs being removed from a state's Medicaid market. We will use the Transformed Medicaid Statistical Information System Analytic Files (TAF), a national Medicaid data file, and collect information about the procurement process, MCO contracts, and per- formance requirements through semi-structured interviews of experts and leaders from states' Medicaid agen- cies and MCOs. Using a difference-in-differences approach, we will investigate the effects of MCO transitions on provider networks (Aim 1) and quality of care as well as health care utilization (Aim 2). Our Aim 3 mixed- methods analysis will bring together quantitative results with qualitative findings of MCO and state character- istics to identify factors that can explain a more or less successful procurement process outcome. This policy- relevant work will provide comprehensive evidence into how state Medicaid agencies can design their MCO pro- curement and monitoring process to improve health care delivery for Medicaid enrollees with SUD.