In this introduction to our book Transatlantic Governance in the Global Economy, we examine the record of transatlantic economic relations, at three levels: the intergovernmental level, where chiefs of government and other high level officials negotiate on behalf of the United States’ and European Union’s respective interests, as determined by internal domestic processes; the transgovernmental level, where lower-level domestic officials work with their transatlantic counterparts on specific issues to coordinate and harmonize domestic policies; and the transnational level, where private actors, including business representatives and other constituents, coordinate efforts to advance their respective goals. Each of these three levels corresponds to a specific body of theory in international relations, including neoliberal regime theory and two-level games, transgovernmental and network approaches, and transnational and global civil society approaches, respectively. We examine two primary sets of questions. First, we seek to explain the development of new and increasingly elaborate mechanisms for transatlantic governance, asking what is new about these mechanisms, and why these actors opted for intensive bilateral cooperation at this time. Put concisely, these three questions ask, “what’s new?” “why transatlantic?” and “why now?” Second, we ask about the nature of cooperation at each of the three levels identified above. Section I places the transatlantic economic relationship in historical and global context. Section II reviews the literature on each of the three theoretical perspectives and provides clear definitions of intergovernmentalism, transgovernmentalism, and transnationalism to guide the analysis. Section III introduces the nine substantive chapters of the volume, divided symmetrically so that three chapters address each level of analysis.