Gerges has been on the trail of the Islamic State (also known as ISIS) since it emerged, under a different name, in the aftermath of the U.S. invasion of Iraq in 2003. The group distinguishes itself from other Salafi-jihadist organizations not primarily through doctrinal differences but rather through its embrace of extreme violence and theatrical beheadings, its hatred of Shiites, and its commitment to hold territory and govern populations as a revived caliphate. It is notable that Ayman al-Zawahiri, who now heads al Qaeda, has denounced ISIS’ poor timing and excessive violence but not its ultimate objectives. Still, isis fights rival jihadists as viciously as it does non-Muslims. In this useful book, Gerges argues that ISIS cannot survive much longer as a military force and, more important, that the group is intellectually impoverished. Moreover, its constituent parts do not share the same interests. But ISIS is the product of an “organic crisis” in Arab politics, Gerges contends, and even if the group collapses, something like it will arise again unless Sunni Muslims reject the ideas and narratives that have allowed the group to flourish.