What will be the consequences of the criminalization of aggression? In 2010, the International Criminal Court made aggression a crime for which individuals can be prosecuted. But questions around what constitutes aggression, who decides, and, most important, how effective this legal change will be in reducing the incidence of war remain. This essay considers these questions in light of two recent books on the criminalization of aggression: Noah Weisbord's The Crime of Aggression: The Quest for Justice in an Age of Drones, Cyberattacks, Insurgents, and Autocrats and Tom Dannenbaum's The Crime of Aggression, Humanity, and the Soldier. While the authors argue in favor of the efficacy of the criminalization of aggression as a means to reduce future war, it is also likely that the criminalization of aggression will reshape war in potentially profound ways.