Previous writers on military change in the early-modern period have defined a military revolution focused on the 17th or even early 18th-centuries. This work suggests that key developments in training, organization, tactics and siege warfare occurred in the 16th century and that, taken together, these innovations constitute a military revolution, changing the face of war. English writers, in their anxiety to spur their compatriots to adopt the new methods, produced some of the most useful manuals of 16th-century Europe. These, together with Italian, Spanish, French and German texts form the main basis of this study, allowing the ideas of contemporaries to be set alongside accounts of actual military conditions in explaining one of the turning points of world military development.