This article considers the contribution of the International Court of Justice (‘ICJ’) to the development of the rules and principles of international humanitarian law (‘IHL’). In recent times, the contribution of the Court to this body of the law has been overshadowed by the work of the two ad hoc international criminal tribunals, the ICTY and the ICTR, established by the Security Council to punish those responsible for serious breaches of IHL. Nevertheless, the ICJ, in both its contentious and advisory jurisdictions, has considered the provisions of IHL on a number of occasions, and in the process has clarified many areas of IHL. This article is concerned with one particular issue: how does the Court perceive the fundamental nature of IHL? The analysis adopts two themes. First, an assessment is made of the part played by the Court in the process of bringing IHL into conformity with the changing emphasis of general international law. In both the Nicaragua case and the Nuclear Weapons Advisory Opinion the Court continued the process of what has been referred to as the “humanization of international law.” Second, the approach of the Court to the vexed issue of the relationship between ius ad bellum and IHL is considered. The conclusion is reached that the approach of the Court to this latter issue has undermined its contribution to infusing the humanitarian ethos into IHL.