Medicaid has entered a period of volatile change, unprecedented in its 51-year history. With 74 million members nationwide,1 Medicaid provides health coverage to more than one in four Americans, ensuring access to healthcare not only for children, pregnant women, the elderly and people with disabilities, but also for an increasing number of low-income working adults. 2017 saw repeated attempts to fundamentally restructure the Medicaid program, and although Congress is likely to turn its attention to other priorities in 2018, federal legislative efforts to revamp Medicaid remain in play. Short of congressional action, vigorous efforts by federal offi cials to use administrative authority to reshape the program is a certainty. And perhaps more than ever before, states will test the limits of their purchasing power and federal fl exibility to make changes to their programs—driven by the desire to improve value, reduce the rate of expenditure growth, and shape the program to meet their policy and political objectives. At the boundaries of these federal and state efforts, expect the courts to weigh in.