| AAC | Aeronautical Administrative Communications |
| AC/WPBX | Advanced Cordless/Wireless Private Branche Exchange |
| ACTS | Advanced Communications Technologies & Services |
| ADEOS | Advanced Earth Exploration Satellite |
| ADM | Administrative |
| ADS | Advanced Digital System |
| ADS | Automatic Dependent Surveillance (USA) |
| AEA | European Airline Association |
| AeFS | Aeronautical Fixed Service |
| AGA | Air-Ground-Air |
| AeM | Aeronautical Mobile Service |
| AeM(OR) | Aeronautical Mobile Service (off-route) |
| AeM(R) | Aeronautical Mobile Service (route) |
| AeMS | Aeronautical Mobile Service |
| AeMSS | Aeronautical Mobile Satellite Service |
| AeMSS(OR) | Aeronautical Mobile Satellite Service (off-route) |
| AeMSS(R) | Aeronautical Mobile Satellite Service (route) |
| AeRNS | Aeronautical Radionavigation Service |
| AeRNSS | Aeronautical Radionavigation-Satellite Service |
| AFSCN | Air Force Satellite Control Network (USA) |
| AIS | Automatic Ship Identification and Surveillance System |
| AmS | Amateur Service |
| AMSAT | Radio Amateur Satellite |
| AMSC | American Mobile Satellite Corporation (USA) |
| AMSS | Aeronautical Mobile-Satellite Service |
| AmSS | Amateur-Satellite Service |
| ANACOM | Autoridade Nacional de COmunicações (Portugal) |
| ANFR | Agence National des Fréquences Radioélectriques (F) |
| ANS | Air Navigation System |
| ANSI | American National Standards Institute (USA) |
| AOC | Aeronautical Operational Control |
| APC | Aeronautical Public Correspondence = TFTS |
| APC | American Personal Communications (USA) |
| APCO | Association of Public-Safety Communications Officials-International, Inc. (USA) |
| API | Advance Publication Information (ITU-R) |
| APRII | Accounting Principles And Regulatory Interconnection Issues (CEPT) |
| APT | Asia-Pacific Telecommunity |
| ARC | Administrative Radio Conference |
| ARFA | Allied Radio Frequency Agency |
| ARIA | Advanced Range Instrumentation Aircraft (USA) |
| ARSR | Air Route Surveillance Radar |
| ART | Authorité de Régulation des Télécommunications (F) |
| ASA | Austrian Space Agency (A) |
| ASDE | Airport Surface Detection Equipment |
| ASK | Amplitude Shift Keying |
| ASMS | Advanced Satellite Mobile Systems |
| ASMS-TF | Task Force on Advanced Satellite Mobile Systems |
| ASO | Australian Space Office (Aus) |
| ASPG | Arab Spectrum Management Group |
| ASTAP | Asia-Pacific Telecommunity Standardization Program (APT) |
| ASTRON | Netherlands Foundation for Research in Astronomy (NL) |
| ASV | Advanced Safety Vehicle System |
| ATC | Air Traffic Control |
| ATC | Ancillary Terrestrial Component |
| ATDRS | Advanced Tracking and Data Relay Satellite |
| ATDRSS | Advanced Tracking and Data Relay Satellite System |
| AT-EZ | Agentschap Telecom – Ministerie Economische Zaken (NL) |
| ATM | Asynchronous Transfer Mode technology |
| ATN | Amateur Television Network (USA) |
| ATNF | Australia Telescope National Facility (Aus) |
| ATU | Arab Telecommunication Union |
| ATS | Air Traffic Services |
| ATV | Amateur Television (USA) |
| AVI | Automatic Vehicle Identification |
| AVM | Automatic Vehicle Monitoring |
| AWACS | Airborne Warning and Control System |