Theories of International Relations take various positions regarding the role of international law in international politics. This article identifies four different perspectives on that role by making two distinctions: first, between approaches that assume that states act on the basis of a cost-benefit analysis and approaches that assume that states act upon shared ideas; second, between theories that assume that sovereign states are the only relevant players in international politics and theories that allow for the possibility that domestic and transnational players may affect international politics as well. Subsequently, the article investigates the choices made by France, Italy, the Netherlands, the United Kingdom and the United States prior to the 2003 war against Iraq. The four perspectives on the role of international law provide different interpretations of the weight these states attached to international law when considering the use of violence against Iraq.