Pre-print, Working paper: The difficult implementation of the Stability and Growth Pact (SGP) during the 2000s can be explained by the low rank of the policy mix in the general process of European integration. Actually the coordination between a common monetary policy and a series of national budgetary policies has emerged rather recently, whereas the extension and deepening of competition on the single market has been the key principle governing the European integration. Since 1999, all the actors have had to readjust their anticipations and strategies about the consequence of the euro: they are in the process of learning how to manage a new policy mix. Various reform proposals of the SGP are presented and discussed. Finally they are related to the nature of the European institutional reforms. The agreement of the European council about the reform of the SGP on March 2005 is interpreted in the light of some major scenarios analyzing the medium-long term evolution of competences in the European Union.