This field manual/Marine Corps warfighting publication establishes doctrine (fundamental principles) for militaryoperations in a counterinsurgency (COIN) environment. It is based on lessons learned from previous counterinsurgenciesand contemporary operations. It is also based on existing interim doctrine and doctrine recentlydeveloped.Counterinsurgency operations generally have been neglected in broader American military doctrine and nationalsecurity policies since the end of the Vietnam War over 30 years ago. This manual is designed to reversethat trend. It is also designed to merge traditional approaches to COIN with the realities of a new internationalarena shaped by technological advances, globalization, and the spread of extremist ideologies-some of themclaiming the authority of a religious faith.The manual begins with a description of insurgencies and counterinsurgencies. The first chapter includes a setof principles and imperatives necessary for successful COIN operations. Chapter 2 discusses nonmilitary organizationscommonly involved in COIN operations and principles for integrating military and civilian activities.Chapter 3 addresses aspects of intelligence specific to COIN operations. The next two chapters discuss thedesign and execution of those operations. Developing host-nation security forces, an essential aspect of successfulCOIN operations, is the subject of chapter 6. Leadership and ethical concerns are addressed in chapter7. Chapter 8, which concerns sustainment of COIN operations, concludes the basic manual. The appendixescontain useful supplemental information. Appendix A discusses factors to consider during the planning, preparation, execution, and assessment of a COIN operation. Appendixes B and C contain supplemental intelligenceinformation. Appendix D addresses legal concerns. Appendix E describes the role of airpower