ISIS does not operate like a typical terrorist group. Unlike Al-Qaeda or the Taliban with a loosely connected network of terrorist cells, ISIS operates like a country with a conventional army.
In January 2014, the secret files of Samir Abd Muhammad al-Khilawi – best-known as Haji Bakr – were obtained after being killed in a firefight. Haji Bakr was a former colonel in the intelligence service of Saddam Hussein's air defense force who later became ISIS' head strategist. He's been secretly pulling the strings at ISIS for years, according to a report by Spiegel.
When he died, he left the blueprint for the Islamic State. These documents show the structure of the Islamic State from top to bottom. This TestTube News video explains how ISIS' chain of command is broken down according to Haji Bakr.