In its recent Wall Opinion, the International Court of Justice gave rather short shrift to Israel's claims that the construction of the wall could be justified as an act of self-defence in the sense of Article 51 United Nations Charter. This article assesses the Court's approach and places it in the broader context of ICJ pronouncements on the use of force. It suggests that the Court failed to appreciate the complex legal problems to which Israel's claim gave rise, in particular the problem of self-defence against attacks by non-state actors. It shows that the Court's restrictive understanding of self-defence, while following the 1986 merits judgment in the Nicaragua case, is difficult to bring in line with modern state practice, and increases the pressure to admit other, non-written, exceptions to Article 2(4) of the UN Charter. © EJIL 2006; all rights reserved.