Counter-terrorism (also spelled counterterrorism) is 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 countries 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.