| Acronym | Meaning |
| IIA | Information Industry Association |
| IIAES | Ion Induced Auger Electron Spectroscopy |
| IIASA | International Institute Of Applied Systems Analysis (near Vienna |
| IID | Ion Impact Desorption |
| IILE | Ion-induced Light Emission |
| IINS | Incoherent Inelastic Neutron Scattering |
| IIR | Isobutylene Isoprene Rubber |
| IIRF | Infinite Impulse Response Filter |
| IIRF | Intergalactic IR Radiation Field |
| IIRS | Ion Impact Radiation Spectroscopy |
| IIRSM | International Institute Of Risk And Safety Management |
| IISCI | Initial Ionic State Comfiguration Interaction |
| IISI | International Iron And Steel Institute |
| IISRP | International Institute Of Synthetic Rubber Producers |
| IITA | Information Infrastructure Technology And Applications |
| IIW | International Institute Of Welding |
| IIXS | Ion Induced X-ray Spectroscopy |
| IJC | International Joint Commission |
| IKBS | Intelligent Knowledge Based Systems |
| IKES | Ion-kinetic-energy Spectroscopy |
| ILAC | International Laboratory Accreditation Cooperation |
| ILAP | Inter-Laboratory Analysis Program |
| ILAS | Improved Limb Atmospheric Spectrometer |
| ILCT | Intraligand Charge-transfer |
| ILD | Interlayer Dielectric |
| ILDA | Intensified Linear Diode Array |
| ILEED | Inelastic Low-energy Electron Diffraction |
| ILIAC | International Library Information And Analytical Center |
| ILIDS | Interferometric Laser Imaging For Droplet Sizing |
| ILK | Integrin-Linked Kinase |
| ILL | Interlibrary Loan |
| ILM | Immobilized Liquid Membrane |
| ILS | Instrumental Line Shape |
| ILS | Intracavity Laser Spectroscopy |
| ILS | Ionization Loss Spectroscopy |
| ILSI | International Life Sciences Institute |
| ILSS | Interlaminar Shear Strength |
| ILTJ | Iodine-Laser Temperature Jump |
| ILWAS | Integrated Lake Water Acidification Study |
| ILZRO | International Lead Zinc Research Organization |
| IMA | International Mineralogical Association |
| IMA | Ion Microanalysis |
| IMAC | Immobilized Metal Ion Affinity Chromatography |
| IMACNMMN | International Mineralogical Assocn. Commission On New Minerals And Mineral Names |
| IMAGE | Imager For Magnetosphere-to-Aurora Global Exploration |
| IMAGE | Integrated Molecular Analysis Of Gene Expression |
| IMAGE | International Monitor For Auroral Geomagnetic Effects |
| IMAGE | Integrated Model To Assess The Greenhouse Effect |
| IMAPS | International Microelectronics And Packaging Society |
| IMAPS | Interstellar Medium Absorption Profile Spectrograph |