The article focuses on the legal questions of International Law concerning the Islamic State, namely its legal qualification and the justifications for the use of force against it, in the absence of both a clear and unambiguous approach of the un Security Council and of a shared position by the doctrine. In the absence of recognition of the Islamic State by the international community and given that the hostingis States maintain their sovereignty, the Islamic State does not constitute, despite its name, a state entity. Since the use of military force against the jihadists of the Islamic State in the territories of Syria and Iraq is not based on Security Council Resolution 2249 of 20 November 2015 and constitutes a breach of Articles 2, paragraph 4, and 51 of the un Charter, the author deems desirable a un Security Council Resolution which expressly authorises the use of force against the Islamic State pursuant to Article 42 of the un Charter in order to refer the unilateral military action of the States within the collective security system of the un Charter.