Historians—both those who concentrate on military history and those who touch upon it in passing—often refer to the ‘laws of war’ in the middle ages without any clear idea of what this term actually implies. Ecclesiastical immunity during warfare has long been held as one such ‘law of war’; this article, however, questions the validity of identifying late medieval ideas of ecclesiastical immunity during wartime as valid ‘law’. The article focuses on English warfare in and around the fourteenth century (c.1290–c.1415), contrasting apparent attempts to protect ecclesiastical property with the widespread destruction of churches, abbeys, and other religious property during wartime. By comparing theoretical military conduct, as stipulated in military ordinances, with actual military conduct in the field, the article seeks to reveal medieval attitudes regarding the limitation of war. A number of English campaigns from Edward I to Henry V are examined, with particular attention given to the Durham Ordinances of Richard II, created on the eve of his 1385 invasion of Scotland. It is argued that notions of ecclesiastical protection contained within military ordinances were based more on politico-military factors than on moral or legal considerations. Furthermore, it is argued, ecclesiastical immunity lacked fundamental characteristics of law—compliance, sanction, enforcement—and therefore cannot be identified as valid ‘law’. [ABSTRACT FROM PUBLISHER]