- AFOSI Air Force Office of Special Investigations (United States)
- AFSA Armed Forces Security Agency (United States)
- ANC African National Congress
- ASIO Australian Security Intelligence Organisation
- AVH Allami Vedelmi Hatosag [Hungarian State Security]
- BCRA Bureau Central de Renseignements et d’Action [Free French Intelligence Service]
- BfV Bundesamt für Verfassungsschutz [Federal German Security Service]
- BIS Bezpecnostni Informacni Sluzba/Security Information Service (Czech Republic)
- BND Bundesnachrichtendienst [Federal German Intelligence Service]
- BOSS Bureau of State Security (South Africa)
- BRUSA Ango-American Signals Intelligence Treaty
- BSC British Security Coordination
- BVD Binnenlandse Veiligheidsdienst (Netherlands)
- CBFE Combined Bureau Far East (Great Britain)
- CESID Centro Superior de Información de la Defensa (Spain)
- CIA Central Intelligence Agency (United States)
- CICI Combined Intelligence Centre Iraq (Great Britain)
- CNI Centro Nationale Información (Chile)
- COMINT Communications Intelligence
- CPGB Communist Party of Great Britain
- CPUSA Communist Party of the United States of America
- CSE Communications Security Establishment (Canada)
- CSO Composite Signals Organisation (Great Britain)
- DCI Director of Central Intelligence (United States)
- DDO Deputy Director for Operations (United States)
- DDP Deputy Directorate for Plans (United States)
- DGI Dirección General de Inteligencia (Cuba)
- DGSE Direction Générale de Sécurité Extérieure [French Intelligence Service]
- DHS Department of Homeland Security (United States)
- DIA Defense Intelligence Agency (United States)
- DIB Delhi Intelligence Bureau (Great Britain)
- DIE Departmentude Informatii Externe [Romanian Intelligence Agency]
- DINA Dirección National de Inteligencia (Chile)
- DIS Defence Intelligence Staff (Great Britain)
- DMI Director of Military Intelligence
- DNI Director of National Intelligence (United States)
- DNI Director of Naval Intelligence
- DO Directorate of Operations (United States)
- DOE Department of Energy (United States)
- DS Drzaven Sigurnost [Bulgarian Intelligence Agency]
- DSIP Dirección de Seguridad e Inteligencia Political (Venezuela)
- DST Direction de la Surveillance du Territoire [French Security Service]
- EOKA Ethniki Organosis Kyprion Agoniston/National
- Organization of Cypriot Combatants
- ETA Euskadi ta Askatascena [Basque Nationalist Organization]
- FBI Federal Bureau of Investigation (United States)
- FBIS Federální Bezpeènostní Informaèní Sluzba/Federal
- Security Information Service (Czech Republic)
- FBIS Foreign Broadcast Information Service (United States)
- FCD First Chief Directorate [of the KGB]
- FLQ Front de Libération du Québec
- FRA Forsvarets Radioanstalt (Sweden)
- FSB Federalnaya Sluzhba Bezopasnosti [Russian Security Service]
- GC&CS Government Code and Cypher School (Great Britain)
- GCHQ Government Communications Headquarters (Great Britain)
- GCR Groupement de Contrôles Radio-éléctrique (France)
- GIS General Intelligence Service (Palestine)
- GRU Glavnoe Razvedyvatel’noe Upravlenye (General Political Administration) [Soviet Military Intelligence Service]
- HUMINT Human Intelligence
- HVA Hauptverwaltung Aufklärung [East German Intelligence Service]
- IDB Inlichtingendienst Buitenland (Netherlands)
- INLA Irish National Liberation Army
- IPI Indian Political Intelligence
- IRA Irish Republican Army
- ISI Inter-Services Intelligence (Pakistan)
- ISLD Inter-Services Liaison Department (Great Britain)
- JIC Joint Intelligence Committee
- JSO Jamahirya Security Organization (Libya)
- KCIA Korean Central Intelligence Agency
- KGB Komitei Gosudarstevnnoi Bezopasnosti [Soviet Intelligence Service]
- KNIS Korean National Intelligence Service
- KPD Kommunistische Partei Deutschland/Communist Party of Germany
- MASINT Measurement and Signature Intelligence
- MfS Ministerium für Staatssicherheit/Ministry of State Security (East Germany)
- MI5 Security Service (Great Britain)
- MI6 Secret Intelligence Service (Great Britain)
- MIT Milli Istihbarat Teskilati/National Intelligence Organization (Turkey)
- MSS Ministry of State Security (China)
- NATO North Atlantic Treaty Organization
- NGA National Geospatial-Intelligence Agency (United States)
- NID Naval Intelligence Division (Great Britain)
- NIE National Intelligence Estimate (United States)
- NIMA National Imagery and Mapping Agency (United States)
- NKVD Narodny Komissariat Vnutrennikh Del’ [Soviet Intelligence Service]
- NOC Non-Official Cover
- NRO National Reconnaissance Office (United States)
- NSA National Security Agency (United States)
- NSC National Security Council (United States)
- NURO National Underwater Reconnaissance Office (United States)
- OAS Organisation Armée Secrète/Secret Army Organization (France)
- OGPU Obyedinennoye Gosudarstvennoye Politicheskoye
- Upravlenye (Unified State Political Administration) [Soviet Intelligence Service]
- OMS Otdel Mezhdunarodnykh Svyazey [Comintern Foreign Relations Department]
- OSS Office of Strategic Services (United States)
- OTP One-Time Pad
- OUP Urzad Ochrony Panstwa [Polish Intelligence Service]
- OVRA Opera Voluntaria per la Repressione Antifascisto [Italian Fascist Security Service]
- PCO Passport Control Officer
- PHOTOINT Photographic Intelligence
- PIDE Policia Internacional e de Defesa do Estado
- [Portuguese Intelligence Service]
- PIRA Provisional Irish Republican Army
- PKK Partiya Karkaren Kurdistan/Kurdistan Workers Party
- PLO Palestine Liberation Organization
- POW Prisoner of War
- PV Positive Vetting
- PWE Political Warfare Executive (Great Britain)
- RAF Royal Air Force (Great Britain)
- RAW Research and Analysis Wing (India)
- RCMP Royal Canadian Mounted Police
- RSS Radio Security Service (Great Britain)
- RUC Royal Ulster Constabulary (Great Britain)
- SAPO Säkerhetspolisen/Security Police (Sweden)
- SAS Special Air Service (Great Britain)
- SAVAK Sazeman-I Effelaat vaAmniyat-I Keshvae/National Organization for Intelligence and Security (Iran)
- SB Sluzba Bezpieczenstwa (Poland)
- SD Sicherheitsdienst [Nazi Security Service]
- SDECE Service de Documentation Extérieure et de Contre-Espionnage [French Intelligence Service]
- SHAEF Supreme Headquarters Allied Expeditionary Force
- SIFE Security Intelligence Far East (Great Britain)
- SIM Servizio Informazioni Militari/Military Intelligence Service (Italy)
- SIME Security Intelligence Middle East (Great Britain)
- SIN Servicio de Inteligencia Nacional (Peru)
- SIS Secret Intelligence Service (Great Britain)
- SIS Special Intelligence Service (United States)
- SISDE Servizio per le Informazioni Generali e la SicurezzaDemocractica [Italian Security Service]
- SISME Servizio per le Informazioni e la Sicurezza Militare [Italian Military Intelligence Service]
- SOE Special Operations Executive (Great Britain)
- SOSUS Sound Surveillance System
- StB Statni Bezpecnost [Czech Intelligence Service]
- SVR Sluzhba Vneshnei Razvedki [Russian Foreign Intelligence Service]
- TELINT Telemetry Intelligence
- UB Urzad Bezpieczenstwa [Polish Intelligence Service]
- UKUSA Anglo-American Signals Intelligence Agreement
- UOUD Urad pro Ochranu Ustavy a Demokracie/Bureau for the Protection of the Constitution and Democracy (Czech Republic)
- UZSI Urad pro Zahranicni Styky a Informace/Bureau for Foreign Contacts and Information (Czech Republic)