This paper relates the main steps of the European Union building from the end of WWII. What may today look like a coherent and well-defined project is in fact the result of numerous steps owing much to contingent circumstances. From ECCS to the treaty of Rome and beyond, the integration of Europe, is in fact as Monnet put it « the sum of the solutions adopted to crises ». Today Europe faces major crises again, especially in the euro zone periphery. Has the step by step Monnet method reached its limits? Nevertheless, it is true that autonomy in an interdependent world is a reactionary illusion.