| Acronym | Meaning |
| ATLEED | Automated Tensor Low-energy Electron Diffraction |
| ATLL | Adult T-cell Leukemia Lymphoma |
| ATM | Aerosol Trajectory Model |
| ATM | Airborne Thematic Mapper |
| ATM | Asynchronous Transfer Mode |
| ATM | Analytic Tetrahedron Method (for Brillouin-zone Integrals And Electron Spin Densities) |
| ATMOS | Atmospheric Trace Molecule Spectroscopy |
| ATMS | Assumption-based Truth Maintenance System |
| ATOC | Acoustic Thermometry Of Ocean Climate |
| ATOFMS | Aerosol Time-of-flight Mass Spectrometry |
| ATP | Adenosine Triphosphate (reg: 56-65-5) |
| ATPASE | Adenosine Triphosphatase |
| ATQW | Asymmetric Triple Quantum Well Structure |
| ATR | Attenuated Total Reflectance |
| ATR-FTIR | Attenuated Total Reflection-Fourier-transform IR Spectroscopy |
| ATRA | All-trans-retinoic Acid |
| ATRP | Atom Transfer Radical Polymerization |
| ATRS | Attenuated Total Reflection Spectroscopy |
| ATS | Applied Technology Satellite |
| ATSDR | Agency For Toxic Substances And Disease Registry |
| ATSR | Along-Track Scanning Radiometer |
| ATTA | Atom Trap Trace Analysis |
| ATTF | Air Toxics Task Force |
| ATTIC | Alternative Treatment Technology Information Center (US EPA) |
| ATW | Accelerator Transmutation Of Waste (for Radioactive Waste) |
| AU | Absorbance Units |
| AU | Astronomical Unit |
| AUBF | Anaerobic Upflow Biofilter |
| AUC | Area Under The Curve |
| AUDM | Advanced Unified Defect Model |
| AUFS | Absorbance Units Full Scale |
| AUHF | Annihilated Unrestricted Hartree-Fock Method |
| AUMP | Annihilated Unrestricted Moeller-Plesset (spin Contaminant) |
| AURA | Association Of Universities For Research In Astronomy |
| AUSB | Aerobic Upflow Sludge Blanket |
| AUSM | Advanced Utility Simulation Model |
| AUSST | Automatic Synthesis Of Symptom Tree Model |
| AUSTRALIS | AMS For Ultra Sensitive Trace Element And Isotope Studies |
| AV | Apparent Viscosity |
| AVA | Anthrax Vaccine Adsorbed |
| AVCC | Average Carbonaceous Chondrites |
| AVCC-IOS | Azimuthal (and) Vibrational Close-coupled (rotational) Infinite Order Sudden |
| AVDP | Analytic Velocity-dependent Potential (for Electron Scattering) |
| AVE | All Valence Electron |
| AVHRR | Advanced Very High Resolution Radiometer (NASA) |
| AVIRIS | Airborne Visible-infrared Imaging Spectrometer |
| AVLIS | Atomic Vapor Laser Isotope Separation |
| AVNIR | Advanced Visible And Near-Infrared Radiometer |
| AVO | Average Virtual Orbital |
| AVP | Arginine Vasopressin |