Beginning with People on War, the ICRC’s ground-breaking global survey in 1999 of the international public’s perceptions and attitudes towards IHL, the book takes a historical approach in examining case studies of the use of empirical assessment in IHL training over the last twenty years. The case studies include the evolution of the ICRC’s approach to IHL training, the views on IHL of newly promoted U.S. Army and Marine Corps majors in the aftermath of 9/11, mental health surveys of U.S. troops deployed to Afghanistan and Iraq that asked searching questions regarding IHL compliance, the remarkably successful battlefield ethics training program that was developed in Iraq to reverse those surveys’ results, and work done with Swiss Military Academy officers, new Malian soldiers, a U.S. Army battalion in Germany, and university students in Ireland and Japan using war video games as an IHL instructional tool. The use of empirical assessment is occurring in the context of evolution in the approach to IHL training, one that increasingly recognizes the vital role played by military leaders in developing a values-oriented culture of compliance with the soldiers in their units.