Estoppel is one of the ‘most powerful and flexible instruments to be found in any system of court jurisprudence’;† and it has featured in the jurisprudence of the International Court of Justice (‘the Court’) and its predecessor, in a number of cases. Estoppel, in the jurisprudence of the Court, obliges a State to be consistent in its attitude to a given factual or legal situation. Such a demand has the potential to encourage stability and predictability in international relations. The Court has not been consistent in the application of estoppel; commentators assert that estoppel lacks coherence in international law. However, few commentators have taken on the task of isolating in what ways the Court has been inconsistent when applying estoppel, and none have made suggestions as to how the Court should eliminate the inconsistencies. Through a detailed examination of the judicial application of estoppel, this paper argues precisely in what ways the Court has been inconsistent, and then makes suggestions as to how the Court should eliminate the inconsistencies. These proposals give estoppel a measure of predictability in the jurisprudence of the Court, and thus ensure that the principle promoting stability does not undermine it. † Sir Frederick Pollock, The Expansion of the Common Law (1904) 108.