The Lisbon Treaty has sparked a new round of debate about the nature of membership in the European Union. Constitutional courts of Germany and the Czech Republic played a prominent role in this debate. Parts of their rulings were framed in the traditional vocabulary of ‘sovereignty’. In this paper, I proceed by showing heuristic limitations of the concept of ‘sovereignty’ in addressing the intricate issue of the EU membership. I will, first, argue that none of the aspects of sovereignty – neither international, nor domestic – is significantly affected by the membership in the Union. Moreover, the sovereignty lenses necessarily put emphasis on the question of the final authority, which legal pluralists rightly reject as misleading in the EU context. This rejection is a result of a genuine “heterarchical” relation between the EU and Member States. As a consequence, the EU membership can be more adequately reconstructed through the constitutional identity lenses. This is what both constitutional courts to a certain extent did in their Lisbon rulings. The German court, in addition, tried to determine the “core areas” of competences beyond which the constitutional identity of Germany as a member state can be compromised within the EU. In the last part of the paper, I will challenge this course of action by demonstrating that it is problematic on a number of accounts. In this respect, the Czech Constitutional Court’s (hereinafter: CCC) approach of refraining from determining in advance and in abstracto what might be the ultimate defining elements of the Czech constitutional identity seems to be more commendable.