This article analyses how the seeds for the development of European law from the 1960s onwards were sown in the foundational treaties. It argues that despite the fact that both European treaties embodied a conscious choice by the majority of the governments not to establish the European Communities on a constitutional basis, a small number of politicians and jurists managed nonetheless to insert the potential for the constitutional practice. Following a chronological account of each set of negotiations, the article untangles the complex ideas and decisions, which crafted both the legal shape of the treaties and the jurisdiction of the new European Court of Justice.