This book is an analysis of Britain's war against Al Qaeda and the phenomenon of international terrorism which marked a paradigm shift in the nature and conduct of war in the twenty-first century. At the heart of the book is an attempt to understand why Britain, which possessed a wealth of experience in the conduct of counterterrorism, counterinsurgency and small wars, developed a strategic and operational design to defeat the Islamist threat which proved to be deeply flawed. In addressing this question the book explores the complex intellectual, doctrinal and geopolitical challenge posed by Al Qaeda and international terrorism and how and why the British response took the form that it did.