| Abwehr | German military intelligence, 1920–45 |
| active measures | Black propaganda, dirty tricks |
| agent | Individual who performs intelligence assignments for an intelligence agency without being an officer or staff member of that agency |
| agent of influence | An agent who is able to influence policy decisions |
| ARCOS | All Russian Co-operative Society, London, 1920–7 |
| asset | A source of human intelligence |
| BSA | Birmingham Small Arms Company |
| C | Chief of the Secret Intelligence Service |
| case officer | An officer of an intelligence agency responsible for operating a particular agent or asset |
| Cheka | Extraordinary Commission for Combating Counter-Revolution and Sabotage, USSR, 1917–22 |
| CIA | Central Intelligence Agency, USA, 1947– |
| CID | Committee of Imperial Defence, London, 1902–39 |
| CIGS | Chief of the Imperial General Staff, London, 1909–64 |
| Comintern | Third Communist International, USSR, 1919–43 |
| CPGB | Communist Party of Great Britain, 1920–91 |
| CPUSA | Communist Party of the United States of America, 1921– |
| cut-out | The intermediary communicating secret information between the provider and recipient of illicit information; knowing the source and destination of the transmitted information, but ignorant of the identities of other persons involved in the spying network |
| dead drop | Prearranged location where an agent, asset or case officer may leave material for collection |
| double agent | Agent cooperating with the intelligence service of one nation state while also working for and controlled by the intelligence or security service of another nation state |
| DPP | Directorate of Public Prosecutions, UK |
| DSO | Defence Security Officer, MI5 |
| FBI | Federal Bureau of Investigation, US law enforcement agency, 1908– |
| FCO | Foreign & Commonwealth Office, 1968– |
| FO | Foreign Office |
| Fourth Department | Soviet military intelligence, known as the Fourth Department of the Red Army’s General Staff, 1926–42 |
| Friend | Source |
| GC&CS | Government Code & Cypher School, 1919–46 |
| GCHQ | Government Communications Headquarters, 1946– |
| GPU | State Political Directorate, USSR, 1922–3 |
| GRU | Soviet military intelligence, 1942–92 |
| HUAC | House Un-American Activities Committee, USA, 1938–69 |
| HUMINT | human intelligence |
| illegal | Officer of an intelligence service without any official connection to the nation for whom he is working; usually with false documentation |
| INO | foreign section of Cheka and its successor bodies, USSR, 1920–41 |
| intelligence agent | An outside individual who is used by an intelligence service to supply information or to gain access to a target |
| intelligence officer | A trained individual who is formally employed in the hierarchy of an intelligence agency, whether serving at home or abroad |
| legal | Intelligence officer serving abroad as an official or semi-official representative of his home country |
| MGB | Ministry for State Security, USSR, 1946–53 |
| MVD | Ministry of Internal Affairs, USSR, 1953–4 (as secret police) |
| negative vetting | background checks on an individual before offering her or him a government job |
| NKGB | People’s Commissariat of State Security, February–July 1941 and 1943–6 |
| NKVD | People’s Commissariat for Internal Affairs (responsible for state security of Soviet Union 1934–February 1941 and July 1941 to 1943) |
| NUPPO | National Union of Police and Prison Officers, 1913–20 |
| OGPU | Combined State Political Directorate, USSR, 1923–34 |
| OSINT | open source intelligence |
| OSS | Office of Strategic Services, Washington, 1942–5 |
| PCO | Passport Control Officer: cover for SIS officers in British embassies and legations |
| positive vetting (PV) | The exhaustive checking of an individual’s background, political affiliations, personal life and character in order to measure their suitability for access to confidential material |
| principal | Intelligence officer directly responsible for running an agent or asset |
| protective security | Security to protect personnel, buildings, documents, communications etc. involved in classified material |
| PUS | Permanent Under Secretary |
| PWE | Political Warfare Executive, UK |
| rezident | Chief of a Soviet Russian intelligence station, with supervisory control over subordinate intelligence personnel |
| rezidentura | Soviet Russian intelligence station |
| ROP | Russian Oil Products Limited |
| SIGINT | Intelligence from intercepted foreign signals and communications. Human intervention is needed to turn the raw product into useful intelligence |
| SIME | Security Intelligence Middle East |
| SIS | Secret Intelligence Service (MI6), 1909– |
| SS | Security Service (MI5, under which name it was founded in 1909), 1931– |
| tradecraft | Acquired techniques of espionage and counterintelligence |
| vorón | Literally ‘raven’: a male Russian operative used for sexual seduction |
