This new textbook seeks to explain how US defense and national security policy is formulated and conducted. The focus is on the role of the President, Congress, political partisans, defense industries, lobbies, science, the media, and interest groups, including the military itself, in shaping policies. It examines the following key themes: US grand strategy; who joins America’s military; how and why weapons are bought; the management of defense; public attitudes toward the military and casualties; the roles of the President and the Congress in controlling the military; the effects of 9/11 on security policy, homeland security, government reorganizations, and intra- and inter-service relations. The book shows how political and organizational interests determine US defense policy, and warns against the introduction of centralising reforms. In emphasizing the process of defense policy-making, rather than just the outcomes of that process, this book signals a departure from the style of many existing textbooks.