The process of European integration has been significantly shaped by law to this day. The European Union (EU) is a legal community with a wide range of powers that not only secures peace but also the self-assertion ("sovereignty") of European states on the world stage. The law also includes the common values of democracy and the rule of law, including the protection of fundamental rights (Art. 2 TEU), which make the EU a community of values. Compliance with common European law ensures the mutual trust between Member States that is necessary for the EU to be able to act. In this respect, in an ever-expanding EU, the question arises as to how implementation deficits can be avoided through more effective cooperation within the European association of states and constitutions (Art. 4(3) TEU) with a view to achieving common goals. At the same time, the federal balance within the association must be maintained and European overreach avoided. What role can the principle of subsidiarity (Art. 5 TEU) and the protection of national constitutional identity (Art. 4(2) TEU) play in this regard? Last but not least, in the wake of enlargement, which is making the EU increasingly heterogeneous, the question arises as to whether its possible overstretching can be countered by a flexible legal framework (core Europe, pioneer groups).