A cornerstone of strategic thinking is a clear understanding of one’s opponent. Developing such an understanding in dealing with the Islamic State (IS) is challenging. Constraints on access to the frontlines in Iraq and Syria make it unusually hard for researchers to ground assessments in evidence‐based approaches. This occasional paper contributes to the development of an empirically grounded understanding of the IS by analyzing the finances and management of the group’s predecessor, the Islamic State of Iraq (ISI), which changed its name to the Islamic State of Iraq and the Levant (ISIL) in April 2013 and then the Islamic State in June 2014.1 There is a direct line of descent from Al‐Qa’ida in Iraq (AQI) through the Islamic State of Iraq to today’s Islamic State, despite changes in the group’s territorial holdings and the announced scale of its ambitions.2 Using historical documents to understand how AQI and the ISI were run can therefore help us better understand the current incarnation of the group, as well as the strengths and weaknesses it may have inherited.