Counterinsurgency (COIN) is "the totality of actions aimed at defeating irregular forces".[1] The Oxford English Dictionary defines counterinsurgency as any "military or political action taken against the activities of guerrillas or revolutionaries"[2] and can be considered war by a state against a non-state adversary.[3] Insurgency and counterinsurgency campaigns have been waged since ancient history. However, modern thinking on counterinsurgency was developed during decolonization.[3] Within the military sciences, counterinsurgency is one of the main operational approaches of irregular warfare.[4]

Police question a civilian during the Malayan Emergency. Counterinsurgency involves action from both military and police authorities.
U.S. Marines and ANA soldiers on patrol during counterinsurgency operations in Marjah, Afghanistan, February 2010

During insurgency and counterinsurgency, the distinction between civilians and combatants is often blurred.[5] Counterinsurgency may involve attempting to win the hearts and minds of populations supporting the insurgency.[6][7] Alternately, it may be waged in an attempt to intimidate[3][8] or eliminate civilian populations suspected of loyalty to the insurgency through indiscriminate violence.[3][9]