| Acronym | Meaning |
| IA | Impulse Approximation |
| IA/PA | Intermediate Alky./partial Alky. |
| IAA | Indole-3-acetic Acid |
| IAAD | Ion Assisted Arc Deposition |
| IAB | Information Access Branch |
| IABO | International Association Of Biological Oceanography (ICSU) |
| IAC | Impregnated Activated Carbon |
| IAC | Immunoaffinity Chromatography |
| IACE | Immunoaffinity Capillary Electrophoresis |
| IACG | Inter-Agency Consultative Group |
| IACIS | International Association Of Colloid And Interface Scientists |
| IACP | Integrated Air Cancer Project |
| IACS | International Annealed Copper Standard |
| IACUC | Institutional Animal Care And Use Committeepar |
| IAD | Ion Assisted Deposition |
| IADN | Integrated Atmospheric Deposition Network |
| IAE | Immunoaffinity Extraction |
| IAEA | International Atomic Energy Agency |
| IAEG | International Association Of Engineering Geology |
| IAEH | International Association For Environmental Hydrology |
| IAES | Ion Excited Auger Electron Spectroscopy |
| IAETL | International Association Of Environmental Testing Laboratories |
| IAG | International Association Of Geodesy |
| IAG | Island-arc Granitoids |
| IAGA | International Association Of Geomagnetism And Aeronomy |
| IAGC | International Association Of Geochemistry And Cosmochemistry |
| IAH | International Association Hydrogeologists |
| IAHE | International Association For Hydrogen Energy |
| IAHR | International Association For Hydraulic Research |
| IAHS | International Association Hydrological Sciences |
| IALLW-CAT | Isotope Area Liquid Low-level Waste Collection And Transfer |
| IAM | Immobilized Artificial Membrane |
| IAM | Independent Atom Model |
| IAM | Integrated Assessment Modeling |
| IAM | Internal Axis Method (in Calcns. Of Rotational Excitation In Atom-mol. Collisions) |
| IAMAP | International Association Of Meteorology And Atmospheric Physics (ICSU) |
| IAMAS | International Association Of Meteorological And Atmospheric Sciences |
| IAP | Intermittent Aeration Process (for Waste Treatment) |
| IAP | Imaging Atom Probe |
| IAP | Immunosuppressive Acidic Protein |
| IAP | Indoor Air Pollution |
| IAP | Inhibitor Of Apoptosis |
| IAP | Integrin-assocd. Protein |
| IAP | Intracisternal A-particle |
| IAP | Ion Activity Products |
| IAP | Islet-activating Protein |
| IAPA | Independent Asymptotic Pair Approxn. (in Electronic Structure) |
| IAPPS | International Association For The Plant Protection Sciences |
| IAPSO | International Association For The Physical Sciences Of The Ocean (ICSU) |
| IAQ | Indoor Air Quality |