The Eurozone crisis has shown that monetary union entails more than just sharing monetary policies. This column, first published on 12 February 2016, identifies four minimal conditions for solidifying the monetary union. In the case of fiscal policy, this means a decentralised solution. In the case of financial supervision and monetary policy, centralisation is unambiguously the appropriate response. In the case of a fourth condition, debt restructuring, either approach is possible, but the authors prefer a solution that involves centrally restructuring debts while allocating costs at national level.