Following the declaration of an Islamic Caliphate in June 2014, ISIS began a concerted period of rebel governance across its Iraqi and Syrian territories until its decline in 2017. How effective ISIS was at governing its territory and the extent to which this effectiveness internally varied
have so far received little attention in the rebel governance literature. Most existing studies extrapolate the group’s governance in its Raqqa and Mosul ‘capitals’ as representative of its entire territory, which leads to important misconceptions about the effectiveness of ISIS’s governance
and prohibits greater understanding of how and why ISIS succeeded in some areas and failed in others. Based on an original database of ISIS primary documents and interviews with both ISIS members and displaced residents of ISIS-controlled areas conducted in Iraq, Lebanon, and Turkey, this paper presents the first comparative analysis of ISIS’s governance effectiveness across the 11 provinces it controlled between 2014 and 2017. I argue that ISIS’s provincial governance effectiveness varied significantly along a scale of none-effective, partially-effective, and fully-effective. The length of time that a province was under ISIS control, religious and ethnic demographics, ISIS's provincial internal governing structure, and the attitude of local residents to previous governing regimes are shown to be significant factors in explaining this variation, amongst others.