Counterterrorism (also spelled counter-terrorism), also known as anti-terrorism, incorporates the practices, military tactics, techniques, and strategies that governments, law enforcement, businesses, and intelligence agencies use to combat or eliminate terrorism. Counterterrorism strategies are a government's motivation to use the instruments of national power to defeat terrorists, the organizations they maintain, and the networks they contain.

If definitions of terrorism are part of a broader insurgency, counterterrorism may employ counterinsurgency measures. The United States Armed Forces uses the term foreign internal defense for programs that support other countries' attempts to suppress insurgency, lawlessness, or subversion, or to reduce the conditions under which threats to national security may develop.