| Abbreviation | Definition |
|---|---|
| ASTA | American Sail Training Association |
| ASTM | American Society for Testing and Materials |
| ASTMH | American Society of Tropical Medicine and Hygiene |
| ASTMH | American Society of Tropical Medicine Hygiene |
| ASTRO | Alarms Submarine Tsunami Relief Operation |
| ASVH | Algemene Senioren Vereniging Houten |
| ASWA | Agavoli Social Welfare Association |
| ASWG | Advisory Statistical Work Group |
| ASWP | Audubon Society of Western Pennsylvania |
| ASYMCA | Armed Services Young Mens' Christian Association of the USA |
| AT | American Trails |
| ATA | American Thyroid Association |
| ATA | American Tinnitus Association |
| ATA | American Transcription Association |
| ATA | Assistive Technologies of Alaska |
| ATAAC | Archives of The Association of American Cultures |
| ATAP | Association of Tech Act Projects |
| atc | anti-platelet Trialists' Collaboration |
| ATC | Appalachian Trail Conference |
| ATC | Appalachian Trail Conservancy |