Situated within the context of the ongoing debate about European contract law, this book provides a detailed examination of the European Union's competence in the field of contract law. It analyses the limits of Union competence in relation to several relevant Treaty provisions which potentially confer competence on the Union to adopt a comprehensive contract law instrument and the exercise of Union competence in connection with the operation of the principles of subsidiarity, proportionality and sincere cooperation. It also explores the viability of several alternative and complementary routes to the adoption of such an instrument, including enhanced cooperation, an intergovernmental treaty and certain American techniques. Setting forth an elaborate account of the context for this debate and its chronological development at the European level, this book charts the discussions relating to the European Union's competence to regulate contract law and offers a comparative analysis of the approach taken to the approximation of contract law in the American setting. Setting forth a detailed account of the context for this debate and its chronological development at the European level, the book charts the discussions that have occurred within and outside the EU relating to the transnational competence to regulate contract law. Situating European constitutional law within the continued debate about European contract law, it also reflects upon the contract law structure of the United States and examines the viability of alternative and complementary routes to the adoption of a comprehensive instrument of substantive contract law.