In this graduation thesis, I will explore supranational constitutionalism in the case of the European Union. At the outset, constitutionalism will be defined as the fundamental concept I will be dealing with throughout this thesis, placing it in different contexts relevant to the issues of constitutional rule in the European Union. We shall see, in which way the national identity is treated as the constitutional category. We shall answer the question of how the idea of „European constitution“ was being developed through time, and on which way is it trying to unite European citizens, no matter the national, religious, culturological, economic and other differences. We shall present the institutional and legal framework under which the government of the European Union operates, and on which way the relations with the member states are organized, what kind of mechanisms are set up as a part of the Treaty on the Functioning of the European Union, which is signed by each member state willing to enter this international organisation during the admission process, what kind of system of value is in place, and on what foundations rests the unification of the European peoples, the problematics of the legitimacy deficit and the series of other, interesting questions. . The exploration developed in this thesis will show what are the features of a supranational constitutionalism contained in the structures, processes and values of the European Union.