This book puts military doctrine into a wider perspective, drawing on military history, philosophy, and political science. Military doctrines are institutional beliefs about what works in war and may be seen as a military's 'software'.Given the trauma of 11 September 2001 and the ensuing War on Terror, serious divergences over what the message of the new military doctrine ought to be were expected around the world. However, such questions were rapidly drowned in ferocious meta-doctrinal disagreements. There was little, if any, agreement on what a doctrine should be, and what it was expected to do for the armed forces. This book aims to provide a theoretical understanding of these arguments, using broader academic perspectives, from philosophy and history. In day-to-day business, most people working with military doctrine do, of course, have an adequate understanding of what it is, but when more fundamental issues arise there is rarely a steady platform to stand on. This opaque and multifarious nature of military doctrine is exactly what makes a study of doctrine and doctrine development particularly intriguing. The most mind-boggling questions are not those concerning the veracity of propositional statements in strategy or the ethical justification of military law, but questions at the intersection of, for example, epistemology, ethics and politics. Hence, the question is rarely whether a particular proposition is true or not, or whether a particular action is ethically justifiable or not, but whether a doctrinal statement is justifiable within a whole set of different considerations, especially theoretical, cultural, and political ones. The aim of this book is thus to give military doctrine a firmer conceptual foundation. It asks: What is actually a military doctrine? Where does it come from, philosophically and historically? How can it be utilised, and what can we expect of it? This book will be of much interest to students of military studies, civil-military relations, strategic studies, and war studies, as well as to students in professional military education.