As the ECJ’s two most famous decisions, Van Gend en Loos and Costa v. ENEL, which established the direct effect and supremacy of European law, are commemorated on their fiftieth anniversaries, attention has also turned to another of the ECJ’s early decisions. On 13th November 1964, in Commission v. Luxembourg & Belgium, the Dairy Products case, the ECJ rejected the use of ‘self-help’ countermeasures in the Community legal order, and therefore marked the fundamental distinction between European law and general international law. Drawing on writings by Robert Lecourt, Paul Reuter, and Paul Kapteyn, this paper demonstrates that a direct causal link between these three cases was recognized by ECJ judges and legal scholars as early as 1965. The historical evidence presented here therefore supports previous comparative analysis that has argued that these three decisions – Van Gend, Costa, and Luxembourg & Belgium – should be acknowledged as profoundly inter-connected, in that national court application of European obligations should be understood as a substitute for the enforcement of European obligations through inter-state countermeasures.