In the United States, the recently enacted Patient Protection and Affordable Care Act of 2010 envisions a significant increase in federal oversight over the nation's health care system. At the same time, however, the legislation requires the states to play key roles in every aspect of the reform agenda (such as expanding Medicaid programs, creating insurance exchanges, and working with providers on delivery system reforms). The complicated intergovernmental partnerships that govern the nation's fragmented and decentralized system are likely to continue, albeit with greater federal oversight and control. But what about intergovernmental relations in the United Kingdom? What impact did the formal devolution of power in 1999 to Scotland, Wales, and Northern Ireland have on health policy in those nations, and in the United Kingdom more generally? Has devolution begun a political process in which health policy in the United Kingdom will, over time, become increasingly decentralized and fragmented, or will this "state of unions" retain its long-standing reputation as perhaps the most centralized of the European nations? In this article, we explore the federalist and intergovernmental implications of recent reforms in the United States and the United Kingdom, and we put forward the argument that political fragmentation (long-standing in the United States and just emerging in the United Kingdom) produces new intergovernmental partnerships that, in turn, produce incremental growth in overall government involvement in the health care arena. This is the impact of what can be called catalytic federalism.