Under Attack makes a new contribution to the field of international relations in general and the study of international law and armed conflict in particular, in two core ways. First, it links information from varying disciplines, most notably international relations and international law, to form a comprehensive picture of state practice and the challenges it poses to the legal rules for the use of force. Secondly, it organises the information in such a way to identify two core groups of contemporary justifications used by states: humanitarian reasons and self-defence, both with their sub-categories. At the core of this book is the question of how state practice since 1990 has challenged the long-established legal regime on the international use of force. Are we merely witnessing a temporary and insignificant challenge to international law or are the rules genuinely under attack?