The article argues that the so-called "new wars" pose a fundamental challenge to international humanitarian law (IHL). Although not historically new, this type of war differs in crucial respects from the conception of war that underlies the traditional paradigm of compliance of IHL. At the heart of this paradigm lie certain assumptions: that IHL embodies a compromise between the interests of the warring parties and humanitarian concerns, and that the warring parties face a number of incentives to comply with the law. The article argues that these assumptions lose their plausibility under the circumstances of the "new wars". As a result, the traditional enforcement mechanisms of IHL invariably fail in these conflicts. The second part of the article discusses the international legal response to the "new wars". In particular, it considers international criminal prosecutions, the activities of the International Committee of the Red Cross and measures by the United Nations Security Council. In the common elements of these measures the article identifies the contours of a new paradigm of compliance in IHL that shifts the emphasis from voluntary compliance to external enforcement.