After a necessary overview of the historical context in which Rolando Quadri’s thought developed, when the European Union was still an eminently economic community, the fundamental lines of Quadri’s thought on the subject are examined and its relevance to today’s world is explored. According to Rolando Quadri’s rigorously pragmatic approach, the European Economic Community did not exceed the limits of an international organization, or rather a supranational organization, distinguished by the power to approve regulations that would be immediately applicable to the internal legal systems of the member states, and which, according to Quadri, lacked sovereignty. The affirmation of the supranational nature of the European Union, as understood by Rolando Quadri, is also reflected in recent reflections by the most authoritative Italian constitutional scholars. More than fifty years later, it can be said that its essential and dogmatic features are difficult to challenge, as the recent history of the European Union unequivocally demonstrates. This is confirmed by Union citizenship, which cannot be assimilated to the status of internal citizenship, the attribution of which defines the people as a constituent element of the State. Rather, it constitutes the attribution by Member States to their citizens of a specific set of rights, the most significant of which is undoubtedly the right to move and reside within the territory of the Member States. The alternative is the evolution towards a true federal state, which has not yet been achieved.