This timely book provides in-depth analytical comparison of the nineteenth century evolution of the American single market with corresponding political, economic, and social developments in post-WWII European efforts to create a single European market. Building the regulatory framework needed for successful adoption of an integrated single market across diverse political units represents one of the most important issues in comparative political economy. What accounts for the political success or failure in creating integrated markets in their respective territories? When social discontent threatens market integration with populist backlash, what must be done to create political support and greater legitimacy? Single Markets focuses on the creation of integrated economies, in which the United States and European Union experienced sharply contested ideas about the operation of their respective markets, conflict over the allocation of institutional authority, and pressure from competing political, economic, and social forces over the role and consequences of increased competition. Drawing upon four case studies, the book highlights the contestation surrounding the US and EUs efforts to create common currencies, expand their borders and territories, and deal with the pressures of populist parties, regional interests and varied fiscal and economic challenges. Theoretically, the book draws on work in European integration and American Political Development (APD) to illustrate that the consolidation of markets in the US and EU took place in conjunction with the expansion of state regulatory power and pressure for democratic reform. Single Markets situates the consolidation of single markets in the US and EU in a broader comparative context that draws on research in economics, public administration, political science, law, and history.