(2019) note, given intense opposition from organized medicine and a lack of institutional capacity, promising reforms that aimed to control costs and improve the quality of care have been routinely shelved. The Patient Protection and Affordable Care Act (ACA), however, has made a number of institutional investments intended to expand government's ability to scale successful demonstration projects into national policy (Guterman et al. 2010). Most important, it consolidated demonstration authority within a new An Engine of Change? The Affordable Care Act and the Shifting Politics of Demonstration Projects phIlIp rocco A nd A ndr ew s. K elly The Patient Protection and Affordable Care Act (ACA) made a number of institutional investments intended to expand the federal government's ability to scale successful demonstration projects into national policy. This article considers how the ACA has reshaped the politics of programmatic innovation in Medicare and Medicaid. A qualitative synthesis of demonstration results suggests that, although the ACA has removed several important veto points to the expansion of successful demonstration projects, numerous barriers to the scaling of reforms remain. These barriers include procedures and techniques that make it difficult to certify the "success" of demonstrations yet make their limitations highly legible. From the analysis, this article draws several lessons for future efforts at delivery-system and payment reform, as well as understandings of policy learning and innovation.