| Acronym | Meaning |
 | ISTC | U.K. Institute Of Scientific And Technical Communications |
| ISTS | Intel Science Talent Search |
| ISU | Integrated Sight Unit - International Skating Union |
| IT | InferoTemporal (neurophysiology) - Information Technology -Italy (FIPS 10-4 Country Code; ISO 3166 Digram) |
| IT | Italian Language (ISO 639-1 Code) |
| ITA | Italian Language (ISO 639-2 Code) |
| ITA | Italy (ISO 3166 Trigram) |
| ITAG | Inertial Terrain-Aided Guidance |
| ITALY | I'll Truly Always Love You |
| ITAS | Improved Target Acquisition Sight |
| ITC | InferoTemporal Cortex (neurophysiology) |
| ITEC | Information Technology Exposition & Conference |
| ITEMS | Interactive Tactical Environment Management System |
| ITER | International Thermonuclear Experimental Reactor |
| ITK | In The Know |
| ITN | Independent Television News (British) |
| ITS | Incompatible Time-sharing System - Individual Training Standards |
| ITT | International Telephone And Telegraph (U.S.) |
| ITTO | International Tropical Timber Organization |
| ITU | Intent-to-Use - International Telecommunication Union (International Telegraph Union 1865-1932) |
| IU | Inuktitut Language (ISO 639-1 Code) |
| IUCN | International Union For The Conservation Of Nature And Natural Resources (World Conservation Union) |
| IUPAC | International Union Of Pure And Applied Chemistry (pronounced Eye-yoo-pac) |
| IUSS | Integrated Undersea Surveillance System - Integrated Unit Simulation System - International Union Of Soil Science |
| IV | C?te D'Ivoire (FIPS 10-4 Country Code; From Ivory Coast) - Four (in Roman Numerals) -IntraVenous (as In Intravenous Drip Or Intravenous Therapy) |
| IVD | Internet Video Device |
| IVECO | Industrial Vehicles Corporation |
| IVF | In Vitro Fertilisation |
| IVI | Interchangeable Virtual Instrument |
| IVIS | Inter-Vehicle Information System |
| IVL | Inter-Visibility Line |
| IVM | In Vitro [Oocyte] Maturation |
| IVO | In Vicinity Of |
| IW | Information Warfare |
| IWARS | Infantry Warrior Simulation |
| IWC | International Whaling Commission |
| IWW | Industrial Workers Of The World |
| IX | Nine (in Roman Numerals) |
| IY | Iraqi-Saudi Neutral Zone (FIPS 10-4 Territory Code; Obsolete 1993) |
| IZ | Iraq (FIPS 10-4 Country Code) |
| J | TENS -Joint-Tactical Exploitation Of National Capabilities |
| J | Joule |
| J1 | Joint [Manpower &] Personnel Directorate |
| J2 | Joint Intelligence Directorate |
| J2EE | Java 2 Platform |
| J2ME | Java 2 Platform |
| J2SE | Java 2 Platform |
| J3 | Joint Operations Directorate |
| J4 | Joint Logistics Directorate |
| J5 | Joint Strategic Plans & Policy Directorate |
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