Today, the dynamics of constitutional powers in the European Union and in each of its Member States are difficult to understand if only one level of government is examined. In other words, within the European Union, the separation of powers for the legislative, the executive and the judicial branches is shaped and must be examined in light of the interdependence and interconnection characterizing the relationships between domestic and supranational legal systems. The article analyses if and how European integration affects the actual functioning of the legislative, executive and judicial powers in national systems, in particular in the context of the mutual interaction with the EU institutions equipped with the same powers, pro quota. The perspective followed in this essay is «procedural», aiming to highlight the influence exerted by the instances of connection and cooperation between levels of government and between constitutional powers. Thus, it provides an assessment of the role and evolution of those powers in the design and development of the procedural linkages and juncturess between the European Union and the Member States, with particular emphasis on the Italian case.