This article shows the influence of functionalism, then neo-functionalism, in the management of the crises that have punctuated the construction of Europe. It focuses in particular on the neo-functionalist engrenage (spillover) process implemented by Jacques Delors during the relaunch of European construction. The article also points out that EMU really began to be envisaged with the departure of General De Gaulle, a politician whom neofunctionalism had little sympathy for. Finally, it shows that, at the time of the Maastricht Treaty, the strong political will to create the euro led to the neglect of two fundamental problems that were to haunt the rest of European construction. First, nothing was really decided on the institutions. Moreover, the choice was made to minimally manage a strong opposition between at least two competing political economy systems: one based on Delors-style subsidiarity and the other on Tietmeyer-style subsidiarity. The result is a conflict between at least these two opposing models of Europe, which the changes brought about by the crises affecting the eurozone have failed to overcome. On precisely these issues, this article looks at ways of bringing points of view closer together while at the same time managing deep-seated divergences whose permanence can also be seen as a source of dynamism. To this end, it proposes a return to Mitrany-style functionalist economic expertise within the framework of Ostrom-style polycentric federalism.