| ANDEVIS AS | Harju |
| Andmekaitse Inspektsioon | Harju |
| Andmevara | Harju |
| ANODA Mobile Development Agency | |
| Antegenes OÜ | |
| Apiko | |
| Applebrie | |
| ApricusIT | |
| Arbonics | |
| Areks | Harju |
| Argus AI | |
| Arounda | |
| Art Media Agency OÜ | Tartu |
| Artec Design OÜ | Harju |
| Artjoker OÜ | |
| Aruandepartner OÜ | |
| Arvutiait OÜ | Harju |
| ArvutiLinn | Harju |
| Arvutiproff OÜ | Harju |
| Arvutiromula | Lääne-Viru |
| AS BCS Itera | Harju |
| AS Datel | Harju |
| AS Koopiakeskus | Harju |
| AS Martem | Harju |
| AS Regio | Harju |
| AS SEB Pank | |
| AS Stallion Ltd | Harju |
| AS Sysdec | Harju |
| AS TBB pank | |
| ASA Quality Services OÜ | Harju |
| ASBIS-Baltik AS | Harju |
| Astonsoft Ltd | Harju |
| Astrec Baltic Ltd | Harju |
| Astri Grup | |
| Asutajate Selts | |
| ATBM | Harju |
| Atihor | |
| Atomic Mail | |
| Atomic Wallet | |
| Attekmi | |
| Attraxia | |
| Audioguide OÜ | |
| Auther.ai | |
| Autobahn Technologies | |
| Autolevi OÜ | |
| Automat BI | |
| Automatio | |
| AuVe Tech OÜ | |
| Avaline Group OÜ | |
| Avalon Soft OÜ | |