How influential are supranational institutions, such as the European Commission, the European Central Bank and the European Commission, in European Union policy making? And how does the influence of these institutions depend on institutional procedures and the preferences of member states? We analyze these classic questions of European Union studies with unique data on 47 contested policy issues that were negotiated during the Eurozone crisis from 2010 to 2015. Our dataset codes the policy outcomes and policy preferences of each member state and of the involved supranational institutions. Exploiting variations in the configurations of member states preferences and of decision making procedures (with different formal involvement of supranational institutions), we empirically analyze with hierarchical models how institutional procedures and member states preferences affect the capacity of supranational institutions to realize their preferred policy outcomes. The findings contribute to the literatures on EU decision making in general, and on the politics of reforming the Eurozone in particular.
