Economic theories point to the potential problems associated with a monetary union but offer limited insights into explaining how the policy is designed. This chapter employs international relations theories to investigate the sources of the main controversies that have characterized policy design reforms, especially those concerning the degree to which provisions constrain states and empower the Council or the Commission. The chapter uses an original dataset of positions on contested issues from 1997 to 2012. In a way that best reflects the recurrent themes of the book, it shows that a host of economic, supranational, and national factors shape positions. Governments with a greater risk of noncompliance prefer greater discretion and governments with higher voting power prefer more Council involvement in enforcement as their risk of noncompliance increases. National public support for the European Union emerges as the most relevant correlate of positions on the Commission’s empowerment: governments facing a more sceptical public display greater reluctance. Other factors, such as governmental ideology, euro area membership, and the sovereign debt crisis, also shape positions.