Retired Brigadier General Kenneth Watkin’s new book, Fighting at the Legal Boundaries: Controlling the Use of Force in Contemporary Conflict, helps address some of the issues with the increasingly blurred line between international humanitarian law and human rights law. Professor Mitt Regan’s review addresses the trends that Watkin regards as posing novel challenges for states accustomed to traditional concepts of the use of force and discusses Watkin’s concepts that are especially relevant to the question of how much the traditional categories of law enforcement guided by human rights principles and armed conflict governed by international humanitarian law should continue to frame thinking about the use of force. Regan also critiques Watkin’s use of the binary framework of law enforcement and armed conflict to guide analysis.