If the qualification of Islamic State of Iraq and Sham (ISIS) actions as a threat for international peace is clearly established, its will to establish a state and a caliphate aren’t inherently internationally illicit: contemporary international law does not determine a process for a state’s birth nor the approval of its existence. It also “ignores” the caliphale institution. However, those two ambitions are blocked by numerous legal obstacles related to the state, its constitutive elements, its territory, its population, its political authority and the relations it maintains, especially regarding the legitimacy of those propositions. Beyond the dimension of territorial and ideological conquest, the ISIS ambition renew otherwise the question related to the adaptability of the state model – and therefore international – for the Muslim community.