| Atreca, Inc. | California |
| ATREG, Inc. | Washington |
| AtreNet, Inc. | California |
| Atrenne Integrated Solutions | Minnesota |
| Atreon Orthopedics | |
| Atreon Orthopedics | |
| AtriCure, Inc. | Ohio |
| Atrility Medical | Wisconsin |
| Atrion Communication Resources, Inc. | California |
| Atris Technology, LLC | Florida |
| Atrium | |
| Atrixware, LLC | Virginia |
| Atropos Therapeutics, Inc. | |
| ATS Internet | New York |
| ATS OnDemand | New Jersey |
| ATS Rocky Mountain | |
| ATS Tech Solutions, Inc. | Georgia |
| AtScale, Inc. | California |
| Atsec Information Security | Texas |
| Atsena Therapeutics | |
| ATSG | New York |
| Attaché, Inc. | Ohio |
| Attachmore Services, LLC | |
| AttackIQ | California |
| AttackIQ, Inc. | California |
| Attagene, Inc. | North Carolina |
| Attain | Virginia |
| Attain Data | Illinois |
| Attalus Capital, L.P. | Pennsylvania |
| ATTCK | New York |
| Attendware | Massachusetts |
| Attensa | Oregon |
| Attention | New York |
| Attention Interactive, Inc. | District of Columbia |
| Attention Software | Colorado |
| Attention Span Media, LLC | |
| Attentive Mobile, Inc. | New Jersey |
| Attentive Science | |
| Attentive.ly | |
| Attentus.Tech | Washington |
| Atticus Pharma, Inc. | |
| Attify, Inc. | |
| Attilanet Corporation | Florida |
| Attitude Online | California |
| Attivare Therapeutics | |
| Attivio | Massachusetts |
| Attivo Networks, Inc. | California |
| ATTO Technology, Inc. | New York |
| Attogene | Texas |
| Attom Solutions | California |