Innovative payment reform initiatives occur in both the public and private sector, but the optimal role in such reforms of the public sector, specifically the Centers for Medicare and Medicaid Services, is up for debate. In this article we examine recent experiences with public-private collaboration on payment and delivery reform and present a framework for determining the role of the government in spurring reform. We argue that as a purchaser, the government should consider the scale and maturity of private-sector activity in determining how to approach designing and implementing payment and delivery system reform. The government can further spur innovation by implementing payment reform for providers less ready to participate in it—such as smaller provider groups with limited organizational and technological capacity to implement reform—through identifying best practices related to attribution models and quality benchmarks and promoting dialogue with the private sector about the testing of new reform programs.