At the end of the twentieth century, academics and policymakers welcomed a trend toward fiscal and political decentralization as part of a potential solution for slow economic growth and poor performance by insulated, unaccountable governments.For the last two decades, researchers have been trying to answer a series of vexing questions about the political economy of multi-layered governance.Much of the best recent research on decentralization has come from close collaborations between university researchers and international aid institutions.As the volume and quality of this collaborative research have increased in recent decades, the time has come to review the lessons from this literature and apply them to debates about future programming.In this volume, the contributors place this research in the broader history of engagement between aid institutions and academics, particularly in the area of decentralized governance, and outline the challenges and opportunities to link evidence and policy action.