| Acronym | Meaning |
| AAHIS | Advanced Airborne Hyperspectral Imaging System |
| AAI | American Association Of Immunologists |
| AAIP | American Association Of Investigative Pathologists |
| AAIT | Atomic Absorption Inhibition Titration |
| AAIW | Antarctic Intermediate Water |
| AAL | Acceptable Ambient Level(s) |
| AALA | American Association For Laboratory Accreditation |
| AAM | Automated Auger Microprobe |
| AAMI | Association For The Advancement Of Medical Instrumentation |
| AAMOM | An Approximate Molecular Orbital Method |
| AAO | Acetaldehyde Oxime |
| AAO | Amino Acid Oxidase |
| AAODL | Atmospheric Aerosols And Optics Data Library |
| AAOE | Airborne Antarctic Ozone Experiment |
| AAOM | American Academy Of Occupational Medicine |
| AAP | Asbestos Action Program |
| AAPCO | Association For American Pesticide Control Officials |
| AAPDI | Anisotropic Atom Point Dipole |
| AAPG | American Association Of Petroleum Geologists |
| AAPM | American Association Of Physicists In Medicine |
| AAPS | American Association Of Pharmaceutical Scientists |
| AAQS | Ambient Air Quality Standard (USEPA) |
| AAR | Association Of American Railroads |
| AAR | Accumulation-area Ratio (for Glaciers) |
| AAR | Alkali-aggregate Reaction |
| AARC | Alliance For Acid Rain Control |
| AAS | Atomic Absorption Spectroscopy |
| AASD | Anaerobic Activated Sludge Digestion |
| AASE | Airborne Arctic Stratospheric Expedition |
| AASHO | American Association Of State Highway Officials |
| AASHTO | American Association Of State And Highway Transportation Officials |
| AASIR | Advanced Atmospheric Sounding And Imaging Radiometer |
| AAT | Aspartate Aminotransferase |
| AAT | Atomic Axial Tensor (in Mol. Optical Properties Calcns.) |
| AATB | American Association Of Tissue Banks |
| AATCC | American Association Of Textile Chemists And Colorists |
| AATSR | Advanced Along-Track Scanning Radiometer |
| AAU | Amendment To Allege Use |
| AAV | Adeno-associated Virus |
| AAW | Air Acetylene Welding |
| AB | Arc Brazing |
| ABA | Abscisic Acid |
| ABA | Acid-base Account [related To Acid-forming Potential] |
| ABA | Acrylonitrile-butadiene Acrylate |
| ABAE | Adult Bovine Aortic Endothelial |
| ABBOT | Atomic Billiard Ball Orbital Theory |
| ABC | ATP-binding Cassette |
| ABC | Absorbing Boundary Condition (green Function) |
| ABC | Avidin-biotin Complex |
| ABCM | Assembly (of) Boundary-controlled Monolayers (method For Electronic-structure Calcns.) |