This article examines the relationship between the concept of sovereignty and the process of European integration. It is argued that the nature of this relationship has been both mutually informative and transformative. As a particular understanding of sovereignty has influenced and determined the perception of European integration, i.e., its conceptualization, so the process of European integration has reflected back on sovereignty and entailed its rethinking. This poses a particular challenge for legal theorists: how to pin down the meaning of sovereignty (...) and European integration so as to put both in the best conceptual and normative light. The article begins by looking at the traditional perspective on sovereignty and how this has been challenged by European integration. The focus then shifts from sovereignty to European integration in order to examine how different perspectives on sovereignty, when used as an epistemic lens for understanding the process of European integration, have produced uneven conceptions of this integration. Finally, the article concludes by making a choice between the various conceptions of sovereignty and European integration. It is argued that the best conception of European integration is offered by the constitutional form of a union founded on pluralist sovereignty. (shrink)