A lot has been written about due diligence in international law and since 1949 the Corfu Channel case is invariably cited as authority for the principle. Yet the concept was far from new to the law of State responsibility when the International Court of Justice (ICJ) handed down its fi rst contentious decision. 1 Through its appreciation of the due diligence principle, the decision has nonetheless served to anchor, if with some dissent and nuance, an objective appreciation of the law of State responsibility. The case equally illustrates the role of the external event (in this case by a third State) in relation to both the subjective and objective elements of the internationally wrongful act. Finally, while an analysis of the due diligence principle as it emerges from the Corfu Channel case is invariably drawn from the fi rst part of the Court’s 1949 decision, the second part of that judgment in fact also bears on the concept. This contribution will conclude by considering this latter aspect of the case.