The Affordable Care Act (ACA) seeks to change fundamentally the U.S. health care system by moving toward universal health insurance coverage. Following a long line of joint state-federal programs in healthcare, it is not surprising that the ACA relies heavily on states to implement several of its key provisions: high-risk insurance pools, health insurance exchanges, and the expansion of Medicaid. The response of states has been diverse and dynamic as some states have made explicit choices about some or all ACA components while others have either steadfastly refused any cooperation or have eagerly sought federal resources to move health reform forward. What explains these dynamic and diverse responses by the states? To answer this question, we examine the decision-making of states concerning the creation of high-risk insurance pools, health insurance exchanges, and the expansion of Medicaid under the ACA. First, we present a brief overview of the ACA and its implications for the use of shared governance. Second, we analyze a series of past health programs involving shared governance, tracing the origin of current arrangements through time. This serves as a guide for our analysis of the ACA and its implications for future health reform. Third, we assess the implementation of the three main programs of health reform requiring state cooperation (high-risk insurance pools, health insurance exchanges, and the expansion of Medicaid) and explain the diverse response of states. Finally, we conclude with implications for future shared governance programs and an outlook for the continuing implementation of health reform.