This field manual establishes doctrine for military operations in a counterinsurgency (COIN) environment. It is based on lessons learned from previous counterinsurgencies and contemporary operations. It is also based on existing interim doctrine and doctrine recently developed. Counterinsurgency operations generally have been neglected in broader American military doctrine and national security policies since the end of the Vietnam War over 40 years ago. This manual is designed to reverse that trend. It is also designed to merge traditional approaches to COIN with the realities of a new international arena shaped by technological advances, globalization, and the spread of extremist ideologies--some of them claiming the authority of a religious faith. This is a comprehensive manual that details every aspect of a successful COIN operation from intelligence to leadership to diplomacy. It also includes several useful appendices that provide important supplementary material.