In this book Uwe Steinhoff describes and explains the basic tenets of just war theory and gives a precise, succinct and highly critical account of its present status and of the most important and controversial current debates surrounding it. Rejecting certain in effect medieval assumptions of traditional just war theory and advancing a liberal outlook, Steinhoff argues that every single individual is a legitimate authority and has under certain circumstances the right to declare war on others or the state. He also argues that the just cause cannot be established independently of the other criteria of jus ad bellum (the justification of entering a war), except for right intention, which he interprets more leniently than the tradition does. Turning to jus in bello (which governs the conduct of a war) he criticises the Doctrine of Double Effect and concludes that insofar as wars kill innocents, and be it as "collateral damage", they cannot be just but at best justified as the lesser evil. Steinhoff gives particular attention to the question why soldiers, allegedly, are legitimate targets and civilians not. Discussing four approaches to the explanation of the difference he argues that the four principles underlying them all need to be taken into account and outlines how their weighing can proceed if applied to concrete cases. The resulting approach does not square the distinction between legitimate and illegitimate targets with the distinction between soldiers and civilians, which has extremely important consequences for the conduct of war. Finally, Steinhoff analyses the concept of terrorism and argues that some forms of "terrorism" are actually no terrorism at all and that even terrorism proper can under certain circumstances be justified. This book is a project of the Oxford Leverhulme Programme on the Changing Character of War.