Alexandre Bernier’s dissertation is the first historical investigation of the interaction between European law and French law based on an extensive use of national, European and private archives. On the one hand, it deals with the penetration of European law into French legal, judicial and academic circles as well as among France’s political and administrative actors. On the other hand, it examines what role these circles and actors played regarding the development and deployment of a new European legal order. By exposing the underlying political tensions behind legal controversies this study demonstrates to what extent the process of interaction between European law and French law was truly affected by the intense rivalry between supporters and opponents of European law in order to gain control of the development of the ECJ’s constitutional practice and, in turn, of its penetration into French law. These two groups (or “trends of thoughts“) were composed of a relatively limited number of legal and institutional actors who often had known each other since World War II. While supporters (alias “the supranationalists“) were politically anchored as Christian Democrats and Socialists, opponents (alias “the sovereignty supporters“) consisted of Gaullists and Socialists. Although the thesis does not provide an exhaustive explanation of European law’s establishment and influence, its description of an ideological and strategic battle between supranationalists and sovereignty supporters does provide possibilities to understand the essential aspects of the interaction between European law and French law in the second half of the 20th century.