Vaughan Lowe has recently argued that the most important task of international lawyers at times of flux is to identify claims with precision.1 In order to accomplish this task with regard to the issue of use of force in Iraq, it seems necessary to review the main American and British arguments, including the formal legal arguments presented, as well as the relevant reactions of other States over a longer period of time. This will allow us to reveal patterns of argumentation, similarities, and differences in the American and British justifications as well as in the responses of the international community.