Espionage, a secret attempt by a government to get closely guarded political, economic, or military information about another nation, especially one that is hostile. In a more general sense, espionage means any kind of spying---by a business competitor, a political group, a law-enforcement agency, or a private individual. This article deals only with international espionage, which is one method of obtaining intelligence (evaluated information) about foreign countries.

Espionage agents are usually called secret agents or spies, though they may rely as much on bribery, impersonation, blackmail, or theft as on secret observation. Their only mission is to get information, not to evaluate it. Some spies are double agents, working for two rival nations. Counterspies try to prevent espionage; their mission is counterespionage, or counterintelligence.

The secret agent, who works inside a foreign country usually alone and at personal peril, generally operates under a cover (an assumed identity) to gain access to secret information. He may deliver information to a contact (another secret agent) or report to his government by secret radio transmission or in person. One common technique is to steal or “borrow” documents, photograph or microfilm them, and send the film out of the country. Secret listening and recording devices are sometimes used to pick up valuable conversations.

In contrast to the methods of the individual spy, espionage can be carried on with long-range electronic detection systems as a group project. Methods include radar surveillance of rocket launchings and airplane traffic, high-altitude telephoto and infrared photography, and the monitoring and recording of communications transmissions. Seacraft, airplanes, and satellites are used generally in this type of espionage. Persons engaged in such projects, as well as in the processing of espionage information, are likely to be technicians, pilots, or other skilled workers rather than traditional secret agents.

Since valuable or secret information is generally in some form of cipher or secret code, espionage systems, therefore, also include cryptographers and cryptanalysts, experts in making and breaking codes and ciphers.

Espionage by the United States is carried out largely through the Central Intelligence Agency (CIA). In addition the CIA supervises and coordinates activities of other United States intelligence agencies. The largest of these is the National Security Agency (NSA), which monitors other nations' communications and breaks and makes codes.

Espionage against the United States is investigated by the Federal Bureau of Investigation (FBI) and prosecuted under direction of the Criminal Division of the Department of Justice. Espionage that aids a wartime enemy is punishable as treason. Espionage that aids foreign countries has been prosecuted under the Espionage Act of 1917 and antisubversion acts.

Russian espionage is carried out chiefly by the Foreign Intelligence Service (formed in 1992) and counterespionage by the Federal Counterintelligence Agency (1993). These are the principal successor agencies to the KGB, the intelligence service of the Soviet Union. Great Britain's main espionage agency is the Secret Intelligence Service---popularly called the British Secret Service, or MI-6. France, Italy, China, and Israel are known to have large espionage networks.


Ancient empires had well-developed espionage networks, and the Old Testament mentions the use of spies by Moses and others. During the 1200's and 1300's the Mongols relied heavily on espionage in their conquests in Asia and Europe. Espionage became highly developed in western Europe in the 1700's and 1800's. It flourished during the French Revolution, under Napoleon, and under the Prussian leaders Frederick the Great and Otto von Bismarck. By World War I, most major powers except the United States had extensive espionage networks.

American espionage during both the Revolutionary War and the Civil War had been confined almost completely to North America. Noted Revolutionary War spies were Nathan Hale on the American side and John Andre on the British side. During the Civil War, Allan Pinkerton organized an intelligence branch for General McClellan's Union armies. The nation's first full-scale espionage system was set up in World War II as part of the Office of Strategic Services (OSS), predecessor to the CIA.

Espionage systems were greatly expanded after World War II as the cold war rivalry intensified between the Western powers and the Communist-bloc countries. In the United States charges of Communist espionage against the nation were common during the late 1940's and early 1950's. One controversial case involved a former State Department official, Alger Hiss. In 1953 Julius and Ethel Rosenberg, charged with giving atomic bomb secrets to the Soviet Union, became the first American civilians to be executed for conspiracy to commit espionage against the United States.

Since the early 1960's espionage has relied heavily on modern technology, especially spy satellites. After the breakup of the Soviet Union in 1991, the major powers cut back on their espionage activities.