Modern military historians struggle to explain medieval strategic behaviour. One key reason, the article argues, is their strong belief in the existence of timeless strategic standards. By analysing the example of the 1415 Agincourt campaign, the article proposes a new approach to understanding late medieval strategy. By reconstructing the normative framework that underpinned strategic practice, the critical importance emerges of an unusual set of conventions which regulated strategy and which allowed for a degree of risk-taking that the traditional and current historiography cannot otherwise explain.