This text explores the enigmas of what intelligence services do, of how their history has been shaped in this century and their impact on the conduct of international relations. Archival exposure and divulging of secrets about intelligence activities in the late 1990s has led to a fascination for the subject among scholars and general readers. With a global approach, the book examines the multiple themes relevant to the analysis of foreign policy and draws on interdisciplinary methods and contributions. The focus is on the British, Soviet and United States intelligence services but attention is also given to less well documented examples such as those in France, Germany, Canada, Australia and Israel. Three unifying themes are employed throughout the book: the concept of a 20th century "intelligence revolution" with dramatic changes in the size, power, scope, professionalism, technology and communications of the major intelligence services, stimulated by the great conflicts of the century; success and failure in the quality of intelligence data and the construction and dissemination of images vital to foreign policy decision-making; and a study of popular culture and its role in establishing patterns of thinking about espionage. The book introduces students to a new generation of work on the secret services and reflects on their future in the 21st century.