The European Union is a compound polity and as such is a constitutionally open regime. A compound polity is a system of multiple separations of powers, organized around anti-hierarchical relations, structured by governance (rather than) government relations. This anti-hierarchical structure is necessary for aggregating state units characterized by different demographic size, economic power, geographical location and political history. The asymmetrical relations between the state components of the polity makes implausible any attempt to foster decision-making processes based on a majority logic. A compound polity is a pluralistic regime necessarily characterized by constitutional pluralism. This constitutional pluralism makes implausible any attempt to give a fixed and permanent constitutional identity to the compound polity. Indeed, due to its very nature, a compound polity is subject to an end-less process of contrasted constitutionalization, in which opposing views of the constitution continuously confront each other. Accordingly the popular rejection of the Constitutional Treaty of the EU in the French and Dutch referenda of, respectively, May and June 2005 might not be an unexpected outcome. Indeed, that outcome signals the structural difficulty to find a definitive solution to the constitutional identity of a compound polity. Mr. Chairman and illustrious members of the scientific committee, let me thank you for the honour of being awarded the prestigious “European Amalfi Prize for the Social Sciences”. However, let me also assure you that I am perfectly aware of your generosity, or better of the limits of my work (and especially of the book, “L’America e i suoi critici”, which prompted your decision). Thinking of the previous winners of the Prize (scholars such as Norbert Elias, Serge Moscovici, Zygmunt Bauman, Ranier M. Lepsius, Wolfgang Mommsen, Charles Tilly, Raymond Boudon, Niklas Luhman, Alain Touraine, Shmuel N. Eisanstadt, Suzanne Keller), a trembling inevitably run through my backbone. As Machiavelli noticed centuries ago, “la Fortuna” is really a blind bird. Being the first Italian scholar to receive the prize, I believe , this award wishes to celebrate? also the Italian community of social scientists and not only my scientific work. This evening, my lectio magistralis will focus on the onstitutionalization of the European Union. I will try to show why the American past might help us to better understand the European future.