Traditionally, the Court of Justice of the European Coal and Steel Community (ECSC) has mainly been considered the somewhat dull predecessor to the more famous Court of Justice of the European Communities, which in 1963-64 ‘constitutionalised’ the Treaties of Rome with the seminal judgments of Van Gend en Loos and Costa V. ENEL. The jurisprudence of the Court of Justice of the ECSC was allegedly conservative dominated by technical and economic considerations less than adventurous activism. Recent historical research has demonstrated the complexity of the legal landscape of the 1950s, in which the legal service of the High Authority from early on promoted a ‘constitutional’ interpretation of European law, but where the member state, as well as most legal experts, still considered European law a subset of international law. How did the Court of Justice of the ECSC manoeuvre between these contradictory tendencies? In what direction did the jurisprudence of the Court develop until 1958? How did the Court function internally? These questions will be addressed on basis of hitherto unused archival documentation that cast new light on the inner development of a Court of Justice of the ECSC and thus on European law in the making.