Under health reform, Medicaid will be expanded to cover nearly all people under age 65 with incomes below 133 percent of the federal poverty line. This issue brief examines how the federal government and the states are expected to split responsibility for financing the expanded Medicaid coverage. For any given state, the share financed by the federal government will vary based on factors such as the state’s Medicaid “matching rate,” coverage decisions prior to the enactment of health reform, and the rate at which eligible people participate in its Medicaid program.