This PhD-project analyses the changing relationship between the European Commission and national governments in the context of fiscal and economic policy coordination. The euro zone and sovereign debt crisis revealed that the institutional setting of policy coordination and surveillance in Economic and Monetary Union was not able to guarantee the stability of the euro zone and prevent negative externalities of national policy action. Therefore, several legislative acts, such as the Six-Pack, the Two-Pack as well as the Treaty on Stability, Coordination and Governance reinforced the provisions for surveillance and enforcement of fiscal and economic policy coordination. The European Commission plays a potentially important role in monitoring, guiding and enforcing policy action. However, competences for economic reform still largely remain in the hands of the Member States and there is until now no consensus among European decision makers over the balance between public investment, structural reform and fiscal consolidation. This PhD-project investigates the manner in which the European Commission uses its powers to cope with the structural problems of Economic and Monetary Union. Actor-centred constructivism provides a useful analytical framework to understand better how the Commission perceives its role and the logic behind how it uses the instruments at its disposal. The added value of the analysis is to provide insights into the relation between the European Commission and national governments within the institutional setting of fiscal and economic policy coordination, thereby addressing a significant lacuna in the academic literature. The findings can potentially inform the current debate over the future of Economic and Monetary Union and could help policy makers to create a more sustainable governance framework for macroeconomic policy coordination.