| Acronym | Meaning |
| ANDA | Abbreviated New Drug Application |
| ANDA | Active Nondestructive Analysis |
| ANDI | Analytical Data Interchange |
| ANEP | Association Of Northwest Environmental Professionals |
| ANF | Atrial Natriuretic Factor |
| ANFO | Ammonium Nitrate Fuel Oil Explosive |
| ANG II | Angiotensin II |
| ANGIS | Australian National Genomic Information Servicepar |
| ANICA | Atmospheric Nutrient Input To Coastal Areas |
| ANITA | Ammonia And Nitrification Analyzer |
| ANK | Al2O3/(Na2O + K2O) |
| ANLL | Acute Nonlymphocytic Leukemia |
| ANM | Asymmetric Nuclear Matter |
| ANMO | Average-natural Molecular Orbital |
| ANMR | Acoustic Nuclear Magnetic Resonance |
| ANN | Artificial Neural Network |
| ANNNI | Axial Next-nearest-neighbor Ising (model Of Superstructure) |
| ANO | Approximate Natural Orbital |
| ANO | Atomic Natural Orbital |
| ANO | Average Natural Orbitals |
| ANOI | Advance Notice Of Intent |
| ANOSIM | Analysis Of Similarity |
| ANOVA | Analysis Of Variation |
| ANP | Atrial Natriuretic Peptide |
| ANPP | Aboveground Net Primary Production |
| ANPP | 4-azido-2-nitrophenyl Phosphate |
| ANPR | Advance Notice Of Proposed Rulemaking |
| ANPR | Atrial Natriuretic Peptide Receptor |
| ANPRM | Advance Notice Of Proposed Rulemaking |
| ANR | Adiabatic Nuclear Rotation (in Calcns. On Mol. Collisions) |
| ANRF | Area Normalization With Response Factors |
| ANRHRD | Air Noise Radiation Health Research Division |
| ANS | Advanced Neutron Source |
| ANS | American National Standard |
| ANS | American Nuclear Society |
| ANS | Autonomic Nervous System |
| ANSI | American National Standards Institute |
| ANSIG | Assignment Of NMR Spectra By Interactive Graphics |
| ANSOM | Apertureless Near-field Scanning Optical Microscopy |
| ANSR | Advanced Neutron Source Reactor |
| ANSTO | Australian Nuclear Science And Technology Organization |
| ANT | Adenine Nucleotide Translocator |
| ANTARES | Australian National Tandem For Applied Research |
| ANTS | 8-aminonaphthalene-1 |
| ANWAP | Arctic Nuclear Waste Assessment Program |
| ANWR | Artic National Wildlife Refuge |
| ANZECC | Australian And New Zealand Environment And Conservation Council |
| AO | Office Of The Administrator |
| AO | Atomic Orbital |
| AOA | Angle Of Attack [propulsion] |