| Acronym | Meaning |
| IECA | International Erosion Control Association |
| IECSC | Inventory Of Existing Chemical Substance In China |
| IECT | Impulsive Ergodic Collision Theory |
| IEDM | International Electron Devices Meeting |
| IEE | Institution Of Electrical Engineers |
| IEEE | Institute Of Electrical And Electronics Engineers |
| IEEM | Ion-electron Emission Microscopy |
| IEET | Intramolecular Electronic Energy Transfer |
| IEF | Isoelectric Focusing |
| IEG | Immediate Early Gene |
| IEH | Intermediate Effective Hamiltonian |
| IEHMO | Iterative Extended Hueckel Molecular Orbital |
| IEHT | Iterative Extended Hueckel Theory |
| IEL | Independent Electron (model In Ion-impact Ionization Calcns.) |
| IEL | Intraepithelial Lymphocyte |
| IEM | Immunoelectron Microscopy |
| IEM | Independent Electron Model (for Ionization In Ion-atom Collisions) |
| IEM | Interstitial Electron Model |
| IEMA | Immunoenzymometric Assay |
| IEMM | Incident Energy Modulation Method |
| IEMP | Integrated Environmental Management Project |
| IEP | Isoelectric Point |
| IEPA | Illinois Environmental Protection Agency |
| IEPA | Independent Electron Pair Approximation |
| IEQ | Indoor Environmental Quality |
| IER | Ion Exchange Resin |
| IERM | Intermediate Energy R-matrix (theory In Scattering Calcns.) |
| IES | Institute Of Environmental Sciences |
| IES | Internal Eliminated Sequence |
| IESS | Inelastic Electron Scattering Spectroscopy |
| IESWTR | Interim Enhanced Surface Water Treatment Rule |
| IETS | Inelastic Electron Tunneling Spectroscopy |
| IEV | Independent Event (model In Ion-atom Collisions) |
| IEV | Ion-exchange Voltammetry |
| IF | Interstitial Free |
| IF DRM | Inversion-free Direct Recursion Method (for Surface Electronic Structure) |
| IFA | Immunofluorescence Assay |
| IFANT | International Foundation For The Advancement Of Nondestructive Testing |
| IFAS | Integrated Fixed-film Activated Sludge |
| IFCC | International Federation Of Clin. Chem. |
| IFD | Industrial Facilities Discharge File (file Within STORET) |
| IFFD | Intermittently Fed Fill And Draw System |
| IFFE | Immune Free Flow Electrophoresis |
| IFM | Immunofluorescence Microscopy |
| IFM | Interfacial Force Microscopy |
| IFMA | Immunofluorometric Assay |
| IFOT | Invariant Fock Operator Technique |
| IFPC | Integrated Flight And Propulsion Control |
| IFPM | Independent Fermi Particle Model (in Atom-ion Impact Ionization) |
| IFPMA | International Federation Of Pharmaceutical Manufacturers Associations |