This short essay, written by a former Chief of the General Staff and a former permanent under-secretary at the Ministry of Defence, seeks to analyse the elements of the just war tradition. The roots of this tradition lie in Christian thinking. The idea of the just war is to be sharply distinguished from that of a holy war, a notion which serves to demonise the enemy. The just war tradition, by contrast, has, as its aim, ‘to control and limit war, sometimes even to forbid it, and always to remember the adversary's humanity’. The authors analyse six criteria for jus ad bellum – the right to fight – a just cause, a proportionate cause, right intention, right authority, a reasonable prospect of success, and war only as a last resort; and two criteria for morality in war itself – jus in bello – discrimination and proportionality in the use of force. The book concludes with a reading list, which could, with advantage, have been longer and have included the works of Augustine and Aquinas. Just war is clearly and incisively written, and would form a good introduction to the topic for sixth-formers and undergraduates as well as the intelligent layperson.