| I | Iodine - One (in Roman Numerals) | - | Astronomy |
| I.E. | Id Est (Latin | - | Astronomy |
| I/ITSEC | Interservice/Industry Training | - | Astronomy |
| I2WD OR I?WD | U.S. Intelligence And Information Warfare Directorate (CERDEC) | - | Astronomy |
| IA | Interlingua Language (ISO 639-1 Code) | - | Astronomy |
| IA | Iowa (postal Symbol) | - | Astronomy |
| IAAF | International Association Of Athletics Federations (International Amateur Athletics Federation From 1912-2001) | - | Astronomy |
| IAAL | I Am A Lawyer | - | Astronomy |
| IAB | International Association For Biologicals | - | Astronomy |
| IACREOT | International Association Of Clerks | - | Astronomy |
| IAD | Ion Assisted Deposition | - | Astronomy |
| IADS | Integrated Air Defence System | - | Astronomy |
| IAEA | International Atomic Energy Agency | - | Astronomy |
| IAF | Industrial Areas Foundation | - | Astronomy |
| IAFG | Information Assurance Focus Group | - | Astronomy |
| IAI | International African Institute - Israel Aircraft Industries | - | Astronomy |
| IANA | Internet Assigned Numbers Authority | - | Astronomy |
| IANAL | I Am Not A Lawyer | - | Astronomy |
| IAQ | Indoor Air Quality - Infrequently Asked Questions | - | Astronomy |
| IAS | Image Assessment System | - | Astronomy |
| IATA | International Air Transport Association | - | Astronomy |
| IAU | International Association Of Universities - International Astronomical Union | - | Astronomy |
| IAUC | International Astronomical Union Circular | - | Astronomy |
| IAW | In Accordance With | - | Astronomy |
| IB | International Baccalaureate | - | Astronomy |
| IBA | Important Bird Area | - | Astronomy |
| IBDM | Information Based Decision Making | - | Astronomy |
| IBDS | Integrated Biological Detection System - International Business Development Specialist | - | Astronomy |
| IBM | International Business Machines | - | Astronomy |
| IBO | Igbo Language (ISO 639-2 Code) | - | Astronomy |
| IBRD | International Bank For Reconstruction And Development (part Of The World Bank) | - | Astronomy |
| IBS | Irritable Bowel Syndrome | - | Astronomy |
| IC | Ice Crystals (METAR Code) - Iceland (FIPS 10-4 Country Code) -Integrated Circuit | - | Astronomy |
| ICANN | Internet Corporation For Assigned Names And Numbers | - | Astronomy |
| ICAO | International Civil Aviation Organization | - | Astronomy |
| ICBM | Intercontinental Ballistic Missile | - | Astronomy |
| ICBN | International Code Of Botanical Nomenclature | - | Astronomy |
| ICC | Integrated Command And Control - International Criminal Court - International Cricket Council - Interstate Commerce Commission | - | Astronomy |
| ICD | Implantable Cardioverter-Defibrillator - Initial Capabilities Document - International Classification Of Diseases | - | Astronomy |
| ICES | International Council For The Explorationof The Seas | - | Astronomy |
| ICF | Intelligent Community Forum | - | Astronomy |
| ICHTHYS | Iesous Christos | - | Astronomy |
| ICM | Improved Conventional Munition - Integrated Collection Management - International Congress Of Mathematicians - Iraq Campaign Medal | - | Astronomy |
| ICMP | Internet Control Message Protocol | - | Astronomy |
| ICNAF | International Commission For The Northwest Atlantic Fisheries (became NAFO In 1978) | - | Astronomy |
| ICNI | Integrated Communication | - | Astronomy |
| ICO | Intermediate Circular Orbit | - | Astronomy |
| ICP | Inductively Coupled Plasma - Insane Clown Posse | - | Astronomy |
| ICRAF | International Centre For Research In Agroforestry (a.k.a. World Agroforestry Centre Since 2002) | - | Astronomy |
| ICRISAT | International Crops Research Institute For The Semi-Arid Tropics | - | Astronomy |
| ICRL | Individual Component Repair List | - | Astronomy |
| ICRS | International Celestial Reference System | - | Astronomy |
| ICS | In-Country Support - Intelligence And Communications Systems - Interim Contractor Support | - | Astronomy |
| ICSI | Intracytoplasmic Sperm Injection | - | Astronomy |
| ICTH | Island Closest To Heaven/Hell Final Fantasy VIII | - | Astronomy |
| ICV | Infantry Carrier Vehicle | - | Astronomy |
| ICW | In Co-ordination With - Indonesia Corruption Watch - Infectious And Chemotherapeutic Waste - Insulating Concrete Wall - Integral Crystalline Waterproofing -Interactive Courseware | - | Astronomy |
| ICZN | International Code Of Zoological Nomenclature - International Commission On Zoological Nomenclature | - | Astronomy |
| ID | Idaho (postal Symbol) -Identity -Indonesia (FIPS 10-4 Country Code; ISO 3166 Digram) -Infantry Division - Intelligent Design | - | Astronomy |
| ID | Indonesian Language (ISO 639-1 Code) | - | Astronomy |
| IDA | U.S. Institute For Defense Analyses - International Development Association (part Of The World Bank | - | Astronomy |
| IDC | International Data Corporation | - | Astronomy |
| IDE | Integrated Development Environment - Integrated Drive Electronics | - | Astronomy |
| IDEA | Individuals With Disabilities Education Improvement Act | - | Astronomy |
| IDF | Israel Defence Forces - Intel Development Forum - International Dairy Federation | - | Astronomy |
| IDL | Interface Definition Language | - | Astronomy |
| IDN | Indonesia (ISO 3166 Trigram) | - | Astronomy |
| IDO | Ido Language (ISO 639-2 Code) | - | Astronomy |
| IDR | Indonesian Rupiah (ISO 4217 Currency Code) | - | Astronomy |
| IE | Indo-European Languages - Internet Explorer -Ireland (ISO 3166 Digram) | - | Astronomy |
| IE | Interlingue Language (ISO 639-1 Code) | - | Astronomy |
| IEA | International Energy Agency | - | Astronomy |
| IEC | International Electrotechnical Commission | - | Astronomy |
| IED | Improvised Explosive Device | - | Astronomy |
| IEEE | Institute Of Electrical And Electronics Engineers (I Triple-E) | - | Astronomy |
| IELTS | International English Language Testing System | - | Astronomy |
| IER | Information Exchange Requirement | - | Astronomy |
| IET | Initial Entry Training | - | Astronomy |
| IETF | Internet Engineering Task Force | - | Astronomy |
| IEW | Intelligence And Electronic Warfare | - | Astronomy |
| IFAH | International Federation For Animal Health | - | Astronomy |
| IFAP | International Federation Of Agricultural Producers | - | Astronomy |
| IFC | International Finance Corporation (part Of The World Bank) -Independent Film Channel | - | Astronomy |
| IFF | Identification | - | Astronomy |
| IFFN | Identification | - | Astronomy |
| IFO | Identified Flying Object (see Also UFO) | - | Astronomy |
| IFOR | UN Implementation Force -Institute For Operations Research - International Fellowship Of Reconciliation | - | Astronomy |
| IFOV | Instantaneous Field Of View | - | Astronomy |
| IFPI | International Federation Of Phonographic Industries | - | Astronomy |
| IFR | Instrument Flight Rules | - | Astronomy |
| IFRB | International Frequency Registration Board | - | Astronomy |
| IFV | Infantry Fighting Vehicle | - | Astronomy |
| IG | Inspector General | - | Astronomy |
| IG | Igbo Language (ISO 639-1 Code) | - | Astronomy |
| IGS | International Ground Station | - | Astronomy |
| IGY | International Geophysical Year | - | Astronomy |
| IHH | Idiopathic Hypogonadotropic Hypogonadism | - | Astronomy |
| IHO | International Hydrographic Organization | - | Astronomy |
| IHR | Institute For Historical Review | - | Astronomy |
| IHÂS | Institut Des Hautes ?tudes Scientifiques (French | - | Astronomy |
