This book discusses ISIS within the context of violent non-state actors (VNSA); analyzes historical, ideological and operational roots and features of the group in Syria; and positions ISIS within the matrix of the conflicting parties in Syria. Although there are aspects of ISIS which do not fully overlap with the definitions of the VNSA, ISIS is still an organization that is on the border of holding qualities of a state in the Westphalian sense. ISIS is the pinnacle of the Salafi-jihadism and takfiri-messianism, and a living example of the Salafi-jihadi’s power of transformation according to changing dynamics on the ground. The group has been particularly skillful in benefitting from chaos by filling in the vacuum left by the failed states, Syria and Iraq. The group’s groundwork was laid down by Abu Musab Al-Zarqawi, who differed both practically and ideologically from Al-Qaeda. The differences between the Al-Zarqawi and Bin Laden schools morphed into active conflict in later periods; as ISIS consolidated its power and began dominating the Salafi-jihadi community. This work demonstrates that ISIS is not a part of the Syrian insurgency against the Assad regime. Rather, it has maintained a separate agenda from the Syrian armed opposition, which has been trying to topple the Assad regime but stay within the existing system. ISIS, to the contrary, rejects the system both politically and territorially in its entirety, and aims to establish a caliphate which has no geographical constraints or limits.