This manual is designed to fill a doctrinal gap. It has been 20 years since the Army published a field manual devoted exclusively to counterinsurgency operations. For the Marine Corps it has been 25 years. With our Soldiers and Marines fighting insurgents in Afghanistan and Iraq, it is essential that we give them a manual that provides principles and guidelines for counterinsurgency operations. Such guidance must be grounded in historical studies. However, it also must be informed by contemporary experiences. This manual takes a general approach to counterinsurgency operations. The Army and Marine Corps recognize that every insurgency is contextual and presents its own set of challenges. You cannot fight former Saddamists and Islamic extremists the same way you would have fought the Viet Cong, Moros, or Tupamaros; the application of principles and fundamentals to deal with each varies considerably. Nonetheless, all insurgencies, even today’s highly adaptable strains, remain wars amongst the people. They use variations of standard themes and adhere to elements of a recognizable revolutionary campaign plan. This manual therefore addresses the common characteristics of insurgencies. It strives to provide those conducting counterinsurgency campaigns with a solid foundation for understanding and addressing specific insurgencies. A counterinsurgency campaign is, as described in this manual, a mix of offensive, defensive, and stability operations conducted along multiple lines of operations. It requires Soldiers and Marines to employ a mix of familiar combat tasks and skills more often associated with nonmilitary agencies. The balance between them depends on the local situation. Achieving this balance is not easy. It requires leaders at all levels to adjust their approach constantly. They must ensure that their Soldiers and Marines are ready to be greeted with either a handshake or a hand grenade while taking on missions only infrequently practiced until recently at our combat training centers. Soldiers and Marines are expected to be nation builders as well as warriors. They must be prepared to help reestablish institutions and local security forces and assist in rebuilding infrastructure and basic services. They must be able to facilitate establishing local governance and the rule of law. The list of such tasks is long; performing them involves extensive coordination and cooperation with many intergovernmental, host-nation, and international agencies. Indeed, the responsibilities of leaders in a counterinsurgency campaign are daunting; however, the discussions in this manual alerts leaders to the challenges of such campaigns and suggest general approaches for grappling with those challenges. Conducting a successful counterinsurgency campaign requires a flexible, adaptive force led by agile, well-informed, culturally astute leaders. It is our hope that this manual provides the guidelines needed to succeed in operations that are exceedingly difficult and complex. Our Soldiers and Marines deserve nothing less.