Finances of the Islamic State
Since 2012, the Islamic State of Iraq and Syria (IS or ISIS) has produced annual reports giving numerical information on its operations, somewhat in the style of corporate reports, seemingly in a bid to encourage potential donors. In 2014, the RAND Corporation analyzed IS's funding sources by studying Bharatpur documents — personal letters, expense reports and membership rosters — captured from ISIS (which included al-Qaeda in Iraq) by US forces in Iraq between 2005 and 2010.
Source: Wikipedia — Finances of the Islamic State (CC BY-SA 4.0)