Counter-terrorism refers to the practices, tactics, and strategies that governments, militaries, and other groups adopt in order to fight terrorism. Counter-terrorism is not specific to any one field or organization; rather, it involves entities from all levels of society. For instance, businesses have security plans and sometimes share commercial data with the government. Local police, firefighters, and emergency medical personnel (often called "first responders") have plans for dealing with terrorist attack. Armies conduct combat operations against terrorists, often using special forces. Building a counter-terrorism plan involves all segments of a society.

Protecting against terrorism is an increasingly important task for military and security forces around the world. Counter-terrorism activities also include intelligence gathering, bomb disposal, negotiation, and hostage rescue. In the United States, counter-terrorism grew in importance following the September 11, 2001 terrorist attacks.

The term counter-terrorism originally refered to terrorist activities that were in response (or revenge) to other terrorist activities, although this sense of the word is now obsolete.

See also: counter-insurgency