Over the first decade of the 21st century, the role of risk-based managed health care for publicly insured beneficiaries has expanded substantially. This report examines this form of health care delivery in 20 states for both Medicaid and CHIP nonelderly adults and children, including people with disabilities. The 20 states were chosen because they include over 80 percent of both Medicaid and CHIP beneficiaries who are enrolled in risk-based managed care. Findings are based on interviews with state Medicaid and CHIP officials, as well as representatives from 40 Managed Care Organizations (MCOs) serving Medicaid and CHIP beneficiaries, and 40 health care providers or provider organizations. In addition, the report contains published data from various sources, including measures of access to care, quality of care, and satisfaction with care over the study period (2001-2010).This review of Medicaid and CHIP risk-based managed care over the first decade of the 21st century shows that well-established programs exist in 19 of the 20 study states (Connecticut being the exception) and that most states are seeking to expand their programs to cover more and higher-cost enrollees. While there is substantial variation across states in approaches, all the study states have developed ways to regularly select plans, define network requirements, and monitor access and quality. In contrast to the early years of development of Medicaid managed care, there is substantial stability in the number and types of plans participating in risk-based managed care. HEDIS and CAHPS data also suggest that preventive care use has improved under risk-based managed care and that beneficiaries are generally satisfied with their health plans. Thus, the risk-based managed care programs that currently exist provide a structure to absorb the newly covered adults under the Affordable Care Act and provide a learning laboratory and important lessons for other states in how to develop an effective risk-based managed care program for Medicaid and CHIP beneficiaries.