Since the mid 19th century, efforts to regulate the conduct of war have steadily increased. In her thought-provoking book Wars of Law, Tanisha Fazal examines the regulation of armed conflict and in particular, the codification of International Humanitarian Law (IHL), the changing nature of IHL, and its multifaceted consequences for wars between and within states. Fazal contends that the decreased involvement of 'law takers' – experts with military backgrounds – in the law-making process, and the growing focus of IHL on the protection of civilians have led states to increasingly try to navigate away from crossing boundaries that would unambiguously commit them to obeying IHL. This, she argues, explains the puzzling decline in rates of formal war declarations and peace treaties in interstate wars. Strikingly, the consequences of IHL for intrastate war are quite different, with some rebel groups eagerly complying with IHL despite its state-centric character. Fazal argues that secessionist rebel groups, due to their aspirations to gain acceptance from the international community, have the greatest tendency to comply with IHL, a trend that could be undercut in the future by the continued lack of reward. Relying on an impressive array of quantitative and qualitative data, and a creative mix of methods ranging from text analysis to interviews and archival research, Fazal documents these and other unintended consequences of 150 years of efforts to regulate war. Ambitious in scope, carefully researched, and highly insightful, this is a must-read for anyone interested in armed conflict and international law.