The Islamic State of Iraq and Levant (Da’esh) has put in place a governance system encompassing judicial structures to justify its grotesque violence. This paper seeks to evaluate the legitimacy of these courts under two complementary perspectives. Whereas establishing courts by an insurgent group during armed conflict should meet the requirements of international humanitarian law (ihl), because Da’esh claims to ground its laws on Islam, these courts should also follow the requirements of Islam as its constituting law. The paper starts with analysing whether international law entitles armed groups to establish their courts. It argues that although such courts are not prohibited at first glance under international law, they should meet the requirements of being regularly constituted while respecting minimum judicial guarantees. Since Da’esh has sought to found its legitimacy on Islam, the paper argues that Da’esh’s interpretation of Islam is not compatible with any major schools of Islamic thought.