Many scholars and policymakers argue that deterrence strategies have no significant role to play in counterterrorism. The case against deterrence rests on three pillars: terrorists are irrational; they value their political ends far above anything deterring states could hold at risk; and they are impossible to find. Each pillar is either incorrect or its implications for deterrence have been misunderstood. Under certain conditions, deterrence is preferable to the use of force. Analysis of the structure of terrorist networks and the processes that produce attacks, as well as the multiple objectives of terrorist organizations, suggests that some deterrence strategies are more effective than those of the past. In particular, many terrorist groups and elements of terrorist support networks can likely be deterred from cooperating with the most threatening terrorist groups, such as al-Qaida. Although the use of force against multiple groups creates common interests among them, an appropriate deterrence strategy could fracture global terrorist networks. The current policy of the U.S. and Philippine governments toward the Moro Islamic Liberation Front (MILF) and the Abu Sayyaf Group illustrates the potential of this approach and the risks of using force. Not only can groups such as the MILF be deterred from cooperating with al-Qaida, they may even be coerced into providing local intelligence on operatives linked to it.