This Report, "Report to Congress: The Evolution of Managed Cared in Medicaid," examines managed care in Medicaid, focusing on the enrollees served, participating plans, spending, payment, access, data, and program accountability. This Report builds upon our March 2011 "Report to the Congress on Medicaid and CHIP," which provided the foundation for a better understanding of the Medicaid and CHIP programs. It served as a starting point for building the analytic framework the Commission will use to assess access, evaluate payment policy, and determine key data needs in future work. The Commission's authorizing language directs MACPAC to focus its June reports to the Congress on "issues affecting Medicaid and CHIP, including the implications of changes in health care delivery in the United States and in the market for health care services on such programs." Medicaid finances health care and related services for about 67 million individuals, including more than 30 million low-income children, more than 10 million persons with disabilities, and 6 million low-income seniors with Medicare. Of these 67 million people, there are approximately 49 million low-income individuals enrolled in some form of Medicaid managed care. Understanding Medicaid managed care arrangements is essential to determining how the program fits into U.S. health care. The Commission's June 2011 Report to the Congress is comprised of two major sections: a baseline description of managed care in Medicaid, and Medicaid and CHIP Program Statistics (MACStats), a standing supplement in MACPAC Reports that provides national and state-specific data on enrollees, spending, and program features. The first section of the Report provides a comprehensive resource on what is known about the use of managed care in Medicaid today, both nationally and at the state level. The majority of states use managed care, and these arrangements are likely to become even more prevalent over the coming years. However, Medicaid managed care programs vary considerably among states, as well as within states, across different populations, and geographic locations. This Report describes the enrollees in Medicaid managed care, including children and families, enrollees with disabilities, and those who are dually eligible for Medicaid and Medicare. The current status of enrollment, payment, access, and quality measurement and improvement is examined, as well as the consistency, availability, and timeliness of data needed to adequately evaluate managed care programs and ensure program accountability. The Commission's June 2011 edition of MACStats presents data on all enrollee groups but highlights enrollment, service use, spending, and characteristics of individuals with disabilities. We focus on these high cost, high need enrollees because they account for a substantial portion of the program's spending, although they are a small share of enrollment. This is a key issue for policymakers as they consider options for controlling spending and improving care management for the complex needs of this population. Moving forward, the Commission plans to examine policies to encourage high quality, efficient care for all enrollees in managed care and in traditional fee for service, especially for those who have complex medical conditions. In addition, the Commission is undertaking research and independent data analysis on access to develop an early-warning system as described in our statutory charge. In this effort, we will work to identify provider shortage areas and other factors that may affect access to care for those enrolled in Medicaid and CHIP.