The laws of war have always been concerned with issues of necessity and proportionality, but how are these principles applied in modern warfare? What are the pressures on practitioners where an increasing emphasis on legality is the norm? Where do such boundaries lie in the contexts, means and methods of contemporary war? What is wrong, or right, in the view of military-political practitioners, in how those concepts relate to today’s means and methods of war? These are among the issues addressed by James Gow in his compelling analysis of war and war crimes, which draws upon research conducted over many years with defence professionals from all over the world. Today more than ever, military strategy has to embrace justice and law, with both being deemed essential prerequisites for achieving success on the battlefield. And in a context where legitimacy defines success in warfare, but is a fragile and contested concept, no group has a greater interest in responding to these pressures and changes positively than the military. It is they who have the greatest need and desire to foster legitimacy in war by getting the politics-law-strategy nexus right, as well as developing a clear understanding of the relationship between war and war crimes, and calibrating where war becomes a war crime.