The most common type of contemporary armed conflict is fought between a state and one or more armed groups, or between two or more armed groups, yet the law regulating non-international armed conflicts has been barely addressed by academics in comparison to the law on international armed conflicts. Moreover, in general, this field of law is analysed on a subsidiary basis, from the point of view of its divergences and gaps as to the latter, rather than systematically and independently. Sandesh Sivakumaran’s book is unique as it focuses solely on the law — understood broadly, not merely as comprising international humanitarian law — applicable to non-international armed conflicts and presents the way such conflicts are regulated as well as the specific rules that constitute this body of law. It thus treats the law of non-international armed conflicts as a whole, including international humanitarian law, international criminal law and international human rights law, which have been traditionally analysed separately. In addition, Sivakumaran clarifies — by adopting a historical perspective on various specific aspects of the regulation of armed conflicts throughout the book — the changes in perspectives and contributions brought by each of these bodies of law, including, but not limited to, humanitarian law applicable to international armed conflicts.