International regulatory relations have commonly been viewed through the prism of international organizations, on the one hand, and international trade disputes, on the other. However, neither of these perspectives offers an adequate understanding of the ways in which international regulatory relations are managed or may be managed more effectively. While the one risks overstating the readiness of states to cede regulatory authority to international institutions, the other risks ignoring the reality of and prospects for cooperative behavior. Transatlantic regulatory cooperation comprises a highly differentiated "bundle" of techniques for reconciling the needs of international trade with the diversity of national regulatory environments and public demands. The processes involved are still poorly understood, due partly to the fact that they have been very largely improvisational, with the result that the framework of regulatory cooperation is still very much a work in progress. Moreover, the main protagonists in this arena -- the US and EU -- have their own well-established domestic regulatory processes with which international initiatives may not readily be integrated, either in terms of values or institutions. While focusing on illustrative sectoral examples of transatlantic regulatory cooperation, this book thus also explores the more general challenge of accommodating regulatory cooperation with domestic legal and political institutions. The volume closes both by calling attention to inescapable legitimacy questions (e.g. reconciliation with principles of democracy and demands for public accountability) and by exploring certain strategic directions and institutional implications for the future.