This study examines how States use legal arguments in cases of armed intervention and how this usage can influence the development of international law. The objective is to contribute to the understanding of the law on armed intervention by conducting a study of how States actually use legal arguments to justify or condemn armed interventions in actual cases. By assessing empirical material within a frame of abstract analysis of possible legal arguments and a pragmatic background of factual and concrete non-legal factors, this study is intended to contribute to the general understanding of the argumentation of States regarding armed interventions. An important aim within this objective is to provide for a wide appreciation of State conduct and argumentation around ideas of legitimacy and legality, primarily regarding the exceptions to the rule of non-use of force in international relations.