This article explores the different ways in which common and civil law traditions have dealt with the unresolved question of unilateral acts of States in international law. To do so, this article focuses on the failed attempt of the International Law Commission to codify the legal regime pertaining to unilateral acts. It is argued that this failure is mainly due to the different approaches taken by members from a common law background and those from civil law background. This article demonstrates that while representatives of the common law legal tradition favoured the idea of viewing such acts as instances of estoppel, those of the civil law legal tradition were prepared to bring unilateral acts within a broader concept of ‘juridical acts’ where the will to be bound is the main criterion for attributing legal effects to them. Both approaches are then tested against the bulk of judicial practice and it is claimed that the civil law approach is more convincing. The author concludes with a call to develop a coherent concept of ‘international juridical acts’ as a standard tool for ascertaining the binding character of unilateral acts.