This chapter finds that MacCormick’s theory of post-sovereignty represents the most sophisticated attempt to date to explain the “pluralistic” nature of Union law, overcoming the simple confrontation of the “European view” and the “national view” of the European Union, which has characterised legal and political scholarship for decades. However, he finds that legal pluralism is not convincing, either as a general theory or as the basis of the re-construction of Union law. This is basically so because it fails to reconstruct the derivative nature of Union law, and cannot provide an adequate framework for deciding conflicts between EC law and national constitutional law. However, MacCormick’s contribution to tackle the difficult and complex problem of the reconstruction of Union law is taken, by Borowski, as the point of departure for what amounts to a sophisticated and revised version of the national theory of constitutional law, namely, Borowski’s derived and nearly unconditional supremacy of Community law. This entails that the actual breadth and scope of the supremacy of Union law is subject to potential exceptions, to be determined by means of weighing and balancing the normative reasons underpinning the claim to supremacy (in concrete, the very weight of European integration) with weighty countervailing reasons which may justify the opposite result in a handful of cases.