Expand: date=January 2007

Counter-terrorism or counterterrorism refers to the practices, tactics, techniques, and strategies that governments, militaries, police departments and corporations adopt in response to terrorist threats and/or acts, both real and imputed.

The tactic of Terrorism is available to insurgents and governments. Not all insurgents use terror as a tactic, and some choose not to use it because other tactics work better for them in a particular context. Individuals, such as Timothy McVeigh, may also engage in terrorist acts such as the Oklahoma City bombing. If the terrorism is part of a broader insurgency, counter-terrorism may also form a part of a counter-insurgency doctrine, but political, economic, and other measures may focus more on the insurgency than the specific acts of terror. Foreign internal defense (FID) is a term used by several countriesFact: date=July 2008 for programs either to suppress insurgency, or reduce the conditions under which insurgency could develop.

Counter-terrorism includes both the detection of potential acts and the response to related events.

Anti-terrorism versus counter-terrorism

The concept of anti-terrorism emerges from a thorough examining of the concept of terrorism as well as an attempt to understand and articulate what constitutes terrorism in Western terms. It must be remembered that in military contexts, terrorism is a tactic, not an ideology. Terrorism may be a tactic in a war between nation-states, in a civil war, or in an insurgency.

Counter-terrorism refers to offensive strategies intended to prevent a belligerent, in a broader conflict, from successfully using the tactic of terrorism. The U.S. military definition, compatible with the definitions used by NATO and many other militaries, is "Operations that include the offensive measures taken to prevent, deter, preempt, and respond to terrorism." In other words, counter-terrorism is a set of techniques for denying an opponent the use terrorism-based tactics, just as counter-air is a set of techniques for denying the opponent the use of attack aircraft.

Anti-terrorism is defensive, intended to reduce the chance of an attack using terrorist tactics at specific points, or to reduce the vulnerability of possible targets to such tactics. "Defensive measures used to reduce the vulnerability of individuals and property to terrorist acts, to include limited response and containment by local military and civilian forces." To continue the analogy between air and terrorist capability, offensive counter-air missions attack the airfields of the opponent, while defensive counter-air uses antiaircraft missiles to protect a point on one's own territory. The ongoing Israeli-Palestinian conflict, Sri Lankan Civil War, and Colombian Civil War are examples of conflicts where terrorism is present, along with other tactics, so that a participant uses counter- and anti-terrorism to limit the opponent's use of terror tactics.