This book assesses and explains the emergence since 2011 of Sunni jihadist organizations in Syria's fledgling insurgency, charts their evolution and situates them within the global Islamist project. Unprecedented numbers of foreign fighters have joined such groups, who will almost certainly continue to host them. Thus, external factors in their emergence are scrutinized, including the strategic and tactical lessons learned from other jihadist conflict zones and the complex interplay between Al-Qaeda and the Islamic State and how it has influenced the jihadist sphere in Syria. Tensions between and conflict within such groups also feature in this indispensable volume.