As insurgent threats evolve and assume new forms, the United States must also evolve in its ability to counter potentially prolonged threats in several parts of the world. Because of the potential for global reach in contemporary insurgencies, the ability to draw on lessons learned from past counterinsurgency (COIN) campaigns using different historical cases can be valuable, helping current and future leaders prevent a repetition of mistakes and building a foundation on which to build contemporary responses. To this end, six historic COIN operations from the 19th and 20th centuries are examined to determine which tactics, techniques, and procedures led to success and which to failure. The Philippines, Algeria, Vietnam, El Salvador, Jammu and Kashmir, and Colombia were chosen for their varied characteristics relating to geography, historical era, outcome, type of insurgency faced, and level of U.S. involvement. Specific issues examined include the counterinsurgents' ability to innovate and adapt, the need to find a way to recognize the threat, and tactics for confronting it.