Medicaid and the State Children's Health Insurance Program (CHIP) are sources of health care coverage for 76 million people, almost one quarter of the population. Medicaid finances health care and related services for more than 30 million low-income children, more than 10 million low-income persons with disabilities, and 6 million low-income seniors with Medicare. CHIP finances health coverage for 8 million uninsured children in families with moderate incomes above Medicaid eligibility levels. This is the first report of the Medicaid and CHIP Payment and Access Commission (MACPAC) to the Congress. The purpose of this initial report is to contribute to a better understanding of the Medicaid and CHIP programs, their roles in the U.S. health care system, and the key policy and data issues to be addressed. This first report also sets out an analytic framework that serves as the foundation for the Commission's future work with respect to access and payment. Also included in the Report is a compilation of Medicaid and CHIP program information, including state-specific information about program enrollment, spending, eligibility levels, Medicaid benefits covered, and the federal medical assistance percentage (FMAP). This section of the Report, called MACStats, will be a standing supplement in all Commission reports to the Congress. The Report is divided into three sections. The first section describes the roles of Medicaid and CHIP in the U.S. health care system and provides overview information for each program. MACStats is the next section, providing Medicaid and CHIP state-specific information and data. The third section of the Report begins a discussion of the Commission's analytic framework for access and payment and identifies key factors the Commission is considering for assessing access, evaluating payment policies, and determining key data needs. This first report to the Congress is foundational and lays the groundwork for recommendations in future reports.