Counterintelligence refers to activities aimed at protecting a nation's intelligence operations from espionage, sabotage, or other forms of interference by foreign entities. It involves identifying and neutralizing threats posed by spies or hostile organizations that seek to gather sensitive information. This field encompasses various techniques, including surveillance, deception, and the recruitment of informants. Agencies like the Federal Bureau of Investigation (FBI) and the Central Intelligence Agency (CIA) in the United States engage in counterintelligence to safeguard national security and maintain the integrity of their operations.