| Atlantic Labs Manager GmbH | |
| Atlantik Networxx GmbH | |
| ATLAS Biolabs GmbH | |
| Atlas Metrics | |
| Atlas-Elektronik GmbH | Bremen |
| ATLAS.ti Scientific Software Development GmbH | Berlin |
| Atlatec | Baden-Württemberg |
| ATM ComputerSysteme GmbH | |
| ATMedia GmbH | Saarland |
| Atmen | |
| ATMINA Solutions GmbH | |
| ATMOS Space Cargo GmbH | |
| ATO interactive GmbH | |
| Atolls GmbH | |
| Atomtigerzoo | North Rhine-Westphalia |
| Atopia Space GmbH | |
| Atoria – the people software GmbH | Baden-Württemberg |
| ATOS Gruppe GmbH & Co. KG | |
| ATOSS Software AG | |
| ATP Elektronik GmbH | Schleswig-Holstein |
| ATR Industrie-Elektronik GmbH | North Rhine-Westphalia |
| Atral-Secal GmbH | Baden-Württemberg |
| atrify GmbH | |
| Atrios | North Rhine-Westphalia |
| Atriva Therapeutics GmbH | |
| Atron Electronic GmbH | Bavaria |
| Atroplan GmbH | Lower Saxony |
| ATS Elektronik GmbH | Lower Saxony |
| Atspace.com | Schleswig-Holstein |
| Attention Insight | |
| Attomol GmbH | |
| AttractSoft GmbH | Schleswig-Holstein |
| ATV Technologie GmbH | |
| Aucobo GmbH | |
| AuCon GmbH | Bavaria |
| Aucoteam GmbH | Berlin |
| AUCOTEC AG | Lower Saxony |
| Aucta GmbH | |
| AuctionTech | |
| Audatic GmbH | |
| audEERING GmbH | |
| Audens Telecommunications | |
| Audibene GmbH | |
| Audicon GmbH | North Rhine-Westphalia |
| Audimex AG | Bavaria |
| Audio Video Elektronik | Thuringia |
| Audiodevel | |
| AUDITcapital GmbH | |
| AuditOne GmbH | |
| Auerbach IT | Saxony |