| Acronym | Meaning |
| IAQINFO | Indoor Air Quality Information Clearinghouse |
| IAQMP | Indoor Air Quality Management Program |
| IAQP | Indoor Air Quality Program |
| IARC | International Agency For Research On Cancer |
| IAS | In-situ Air Sparging |
| IAS | Inelastic Atom Scattering |
| IAS | Isobaric Analog States |
| IASAP | International Arctic Seas Assessment Project |
| IASC | International Arctic Science Committee |
| IASCC | Irradiation-assisted Stress-corrosion Cracking |
| IASH | International Association On The Stability And Handling Of Liquid Fuels |
| IASI | Infrared Atmospheric Sounding Interferometer |
| IASPEI | International Association Of Seismology And Physics Of The Earth's Interior |
| IAST | Ideal Adsorbed Soln. Theory |
| IAT | Island Arc Tholeiite |
| IATA | International Air Transport Association (Geneva |
| IAVCEI | International Association Of Volcanology And Chemistry Of The Earth's Interior |
| IAVI | International AIDS Vaccine Initiative |
| IAWPRC | International Association For Water Pollution Research And Control |
| IAWQ | International Association On Water Quality |
| IBA | Ion Beam Analysis |
| IBAC | Immobilized Biomembrane Affinity Chromatography |
| IBAD | Ion-Beam-Assisted Deposition |
| IBAE | Ion Beam Assisted Etching |
| IBARE | Ion Beam Assisted Radical Etching |
| IBD | Inflammatory Bowel Diseases |
| IBD | Ion Beam Deposition |
| IBI | Index Of Biotic Integritypar |
| IBIC | Ion Beam Induced Charge |
| IBICC | Ion Beam Induced Charge Collection |
| IBICVD | Ion Beam Induced Chemical Vapor Deposition |
| IBIL | Ion Beam Induced Luminescence |
| IBM | International Business Machines |
| IBMK | Isobutyl Methyl Ketone |
| IBMS | Ion Beam Mass Spectrometry |
| IBR | In-plane Birefringence |
| IBR | Infectious Bovine Rhinotracheitis |
| IBS | Incomplete Basis Set |
| IBS | Ion Backscattering Spectroscopy |
| IBS | Ion Beam Sputtering |
| IBS | Irritable Bowel Syndrome |
| IBSCA | Ion Beam Spectrochemical Analysis |
| IBV | Infectious Bronchitis Virus |
| IC | Integrated Circuit |
| IC | Ion Chromatography |
| IC-ACPF | Internally Contracted (multireference) Averaged Coupled Pair Functional |
| ICAC | Institute Of Clean Air Companies |
| ICACGP | International Commission On Atmospheric Chemistry And Global Pollution |
| ICAM | Integrated Climate Assessment Model |
| ICAM | Intercellular Adhesion Molecule |