| AQ Manager | Walloon Brabant |
| Aquilon Pharmaceuticals S.A. | |
| ARCHE Consulting | |
| Archer Research | |
| ArchiSnapper | |
| Arco information | Antwerp |
| Arco Linux | Antwerp |
| ARCSOM | |
| Ardena Holding N.V. | |
| Ardis | East Flanders |
| ARDIS Information Systems N.V. | |
| AreTheyHappy N.V. | |
| argenx B.V. | |
| Argon7 | Walloon Brabant |
| ArKaos | Walloon Brabant |
| Arkite | |
| Arpaweb | Namur |
| Arpege Music | |
| Art Vision International BVBA | Antwerp |
| Arteïa | |
| Arteveldehogeschool Gent | |
| Artialis S.A. | |
| ArtiQ | |
| ArtWhere | Walloon Brabant |
| ASCI N.V. | East Flanders |
| Aseptic Technologies | |
| ASP | Brussels-Capital |
| Aspect Analytics | |
| Assusoft | |
| ASTRID | Brussels-Capital |
| AstriVax | |
| ATB therapeutics | |
| Athena Computer Services | Liège |
| ATiT Audiovisual Technologies, Informatics and Telecommunications | Flemish Brabant |
| ATM-PRO | Walloon Brabant |
| Atomikos B.V.B.A. | Antwerp |
| Aucenanne | Hainaut |
| Audaxis | Walloon Brabant |
| Augustine Therapeutics | |
| Aurelium | Antwerp |
| Aurora Labs | |
| Automation N.V. | Flemish Brabant |
| Autorité de la protection des données | Brussels-Capital |
| Autorité des services et marchés financiers | |
| Aviate Labs | |
| AvioBook | |
| Aware N.V./S.A. | |
| Awell | |
| Axiles Bionics | |
| AxonJay | |