Since Ibrahim Awad Ibrahim al-Badri, under his nom de guere Abu Bakr al-Baghdadi, declared the establishment of a worldwide caliphate on 29 June 2014 from the Nur al-Din Zenki Mosque in Mosul, Iraq, dozens of books have been written seeking to explain the rapid rise and breathtaking brutality of the Islamic State group. There is a certain “all hands on deck” feel to the flood of commentary on ISIS—journalists, academics, policy wonks, military figures, analysts, and politicians all have had their say. The visibility of the group, augmented by the rhetorical use to which they have been put by unrelated political debates, have perhaps made this inevitable. The four books reviewed here are part of this trend, and their collective strength is in their breadth and factual detail. There is information aplenty, and all the books included in this review do an admirable job, each in its own way, of detailing the history of the organization. The Islamic State group's deft use of online propaganda, its place in the post-9/11 jihadi landscape, its territorial gains and losses, and its prodigious ability, until recently, to draw large numbers of recruits into Syria or online support roles, have all received detailed treatment.