List of acronyms: I

(Main list of acronyms)


 * I – (s) Iodine – One (in Roman numerals)

I0–9

 * I2WD or I2WD – (i) U.S. Intelligence and Information Warfare Directorate (CERDEC)

IA

 * ia – (s) Interlingua language (ISO 639-1 code)
 * IA – (s) Iowa (postal symbol)
 * IAAF – (i) International Association of Athletics Federations ("International Amateur Athletics Federation" from 1912 to 2001; renamed "World Athletics" in 2019)
 * IAAL – (i) I Am A Lawyer
 * IAAS - (p) Infrastructure-as-a-Service
 * IAB –
 * (i) International Association for Biologicals
 * IATA code of McConnell Air Force Base
 * IACREOT – (i) International Association of Clerks, Recorders, Election Officials, and Treasurers
 * IAD –
 * (i) Ion Assisted Deposition
 * IATA code for Washington Dulles International Airport
 * IADS – (i) Integrated Air Defence System
 * IAE - (i) International Aero Engines (aircraft engine joint venture)
 * IAEA – (i) International Atomic Energy Agency
 * IAF
 * {i} Industrial Areas Foundation
 * (i) Israeli Air Force
 * IAFG – (i) Information Assurance Focus Group
 * IAI –
 * (i) International African Institute
 * Israel Aircraft Industries
 * IANA – (i) Internet Assigned Numbers Authority
 * IANAL – (i) I Am Not A Lawyer
 * IAPD
 * International Associates of Paediatric(sic) Dentistry
 * (i) Investment Adviser Public Disclosure
 * iShares Asia Pacific Dividend
 * IAQ – (i) Indoor air quality – Infrequently Asked Questions
 * IAS – (i) Image Assessment System
 * IASIP – (i) It's Always Sunny in Philadelphia
 * IATA – (a/i) International Air Transport Association
 * IATF – International Automotive Task Force
 * IATSE – International Alliance of Theatrical Stage Employees
 * IAU – (i) International Association of Universities – International Astronomical Union
 * IAUC – (i) International Astronomical Union Circular
 * IAW – (i) In Accordance With

IB

 * IB – (i) International Baccalaureate
 * IBA – (i) Important Bird Area
 * IBD – (i) Inflammatory Bowel Disease
 * IBDM – (i) Information Based Decision Making
 * IBDS – (i) Integrated Biological Detection System – International Business Development Specialist
 * IBF - International Boxing Federation
 * IBGe – (i) Isobutylgermane
 * IBGE – (i) Instituto Brasileiro de Geografia e Estatística (Portuguese, "Brazilian Institute of Geography and Statistics")
 * IBHOF - International Boxing Hall of Fame
 * IBM – (i) International Business Machines
 * ibo – (s) Igbo language (ISO 639-2 code)
 * IBRD – (i) International Bank for Reconstruction and Development (part of the World Bank)
 * IBS – (i) Irritable Bowel Syndrome

IC

 * IC
 * (s) Ice Crystals (METAR Code)
 * Iceland (FIPS 10-4 country code)
 * (i) Integrated Circuit - [inner circle]
 * ICANN – (a) Internet Corporation for Assigned Names and Numbers
 * ICAO – (i) International Civil Aviation Organization
 * ICBM – (i) Intercontinental Ballistic Missile
 * ICBM – I see (phonetically "c") BatMan
 * ICBN – (i) International Code of Botanical Nomenclature
 * ICC
 * (i) Integrated Command and Control
 * International Criminal Court
 * International Cricket Council
 * Interstate Commerce Commission
 * International Chamber of Commerce
 * ICD
 * (i) Implantable Cardioverter-Defibrillator
 * Initial Capabilities Document
 * International Classification of Diseases
 * ICE
 * (i/a) (U.S.) Immigration and Customs Enforcement
 * In case of emergency
 * Internal Combustion Engine (Vehicles)
 * ICES – (a/i) International Council for the Exploration of the Sea
 * ICF – (i) Intelligent Community Forum
 * ICHTHYS – (a) Iesous Christos, Theou Yios, Soter (Greek, "Jesus Christ, Son of God, Savior")
 * ICM
 * (i) Improved Conventional Munition
 * Integrated Collection Management
 * International Congress of Mathematicians
 * Iraq Campaign Medal
 * ICMP – (i) Internet Control Message Protocol
 * ICNAF – (i) International Commission for the Northwest Atlantic Fisheries (became NAFO in 1978)
 * ICNI – (i) Integrated Communication, Navigation, and Identification
 * ICO – (i) Intermediate Circular Orbit
 * ICP
 * (i) Inductively coupled plasma
 * Insane Clown Posse
 * ICPE – (a/i) International Conference on Pharmacoepidemiology, the annual conference of the International Society for Pharmacoepidemiology
 * ICRAF – (i) International Centre for Research in Agroforestry (a.k.a. World Agroforestry Centre since 2002)
 * ICRISAT – (i/a) International Crops Research Institute for the Semi-Arid Tropics
 * ICRL – (i) Individual Component Repair List
 * ICRS – (i) International Celestial Reference System
 * ICS
 * (i) In-Country Support
 * Intelligence and Communications Systems
 * Interim Contractor Support
 * ICSI – (p) Intracytoplasmic Sperm Injection
 * ICT – (i) Information and communication technologies
 * ICTH – (i) Island Closest to Heaven/Hell Final Fantasy VIII
 * ICV – (i) Infantry Carrier Vehicle
 * ICW
 * (i) In Co-ordination With
 * Indonesia Corruption Watch
 * Infectious and Chemotherapeutic Waste
 * Insulating Concrete Wall
 * Integral Crystalline Waterproofing
 * (p) Interactive Courseware
 * (i) International Championship Wrestling (defunct US professional wrestling promotion)
 * ICYMI – (i) In Case You Missed It
 * ICZN
 * (i) International Code of Zoological Nomenclature
 * International Commission on Zoological Nomenclature

ID

 * id – (s) Indonesian language (ISO 639-1 code)
 * ID
 * (s) Idaho (postal symbol)
 * (p) Identity
 * (s) Indonesia (FIPS 10-4 country code; ISO 3166 digram)
 * (i) Infantry Division
 * Intelligent Design
 * ID10T Error – (i) Idiot User Error (IT help desk inside joke)
 * IDA
 * (i) U.S. Institute for Defense Analyses
 * International Development Association (part of the World Bank
 * IDC – (i)
 * International Data Corporation
 * "I Don't Care"
 * IDDI – (i) I don't do initialisms (see irony)
 * IDE
 * (i) Integrated Development Environment
 * Integrated Drive Electronics
 * IDeA – (a) Improvement and Development Agency, the former name of Local Government Improvement and Development in the United Kingdom
 * IDEA
 * (a) Individuals with Disabilities Education Act (U.S.)
 * International Data Encryption Algorithm
 * International Design Excellence Awards
 * IDF
 * (i) Israel Defense Forces
 * Intel Development Forum
 * International Dairy Federation
 * IDGAF – (i) I don't give a f**k
 * IDK – (i) I don't know
 * IDKIBTI – I don't know, I'm black, that's it
 * IDL – (i) Interface Definition Language
 * IDN – (s) Indonesia (ISO 3166 trigram)
 * ido – (s) Ido language (ISO 639-2 code)
 * IDR – (s) Indonesian rupiah (ISO 4217 currency code)
 * IDTS – (i) I don't think so

IE

 * i.e. – (i) id est (Latin, roughly "that is")
 * ie – (s) Interlingue language (ISO 639-1 code)
 * IE – (i) Indo-European languages – Internet Explorer – (s) Ireland (ISO 3166 digram) – Iced Earth
 * IEA – (i) International Energy Agency
 * IEC – (i) International Electrotechnical Commission
 * IED – (i) Improvised Explosive Device
 * IEEE – (p) Institute of Electrical and Electronics Engineers ("I triple-E")
 * IELTS – (a) International English Language Testing System
 * IER – (i) Information Exchange Requirement
 * IET – (i) Institution of Engineering and Technology
 * IET – (ii) Initial Entry Training
 * IETF – (i) Internet Engineering Task Force
 * IEW – (i) Intelligence and Electronic Warfare

IF

 * IFAB – (i) International Football Association Board
 * IFAH – (i) International Federation for Animal Health
 * IFAP – (i) International Federation of Agricultural Producers, (i) International Fashion Academy Pakistan
 * IFC – (i) International Finance Corporation (part of the World Bank) – (a) Independent Film Channel
 * IFF – (i) Identification, Friend or Foe – Individually Fresh Frozen – International Flavors and Fragrances
 * IFFN – (i) Identification, Friend, Foe, or Neutral
 * IFO – (i) Identified Flying Object (see also UFO)
 * IFOR – (p) UN Implementation Force – (i) Institute for Operations Research – International Fellowship of Reconciliation
 * IFOV – (i) Instantaneous Field of View
 * IFPI – (i) International Federation of Phonographic Industries
 * IFR – (i) Instrument Flight Rules
 * IFRB – (i) International Frequency Registration Board
 * IFV – (i) Infantry Fighting Vehicle

IG

 * ig – (s) Igbo language (ISO 639-1 code)
 * IG –
 * (i) Inspector General
 * Instagram
 * IGFA – International Game Fish Association
 * IGM - IATA code for Kingman Airport
 * IGNOU – (a) Indira Gandhi National Open University
 * IGS – (i) International Ground Station
 * IGY – (i) Israeli Gay Youth – International Geophysical Year

IH

 * IHÉS – (i) Institut des Hautes Études Scientifiques (French, Institute of Advanced Scientific Studies)
 * IHH – (i) Idiopathic Hypogonadotropic Hypogonadism
 * IHO – (i/a) International Hydrographic Organization
 * IHOP – (i/a) International House of Pancakes, the original name of this American restaurant chain ("EYE-hop")
 * IHR – (i) Institute for Historical Review
 * IHSI – Institutum Historicum Societatis Iesu (Jesuit Historical Institute)

II

 * ii – (s) Sichuan Yi language (ISO 639-1 code)
 * II – (s) Two (in Roman numerals)
 * IICA – (i) Inter-American Institute for Cooperation on Agriculture
 * IIE – (i) Innovative Interstellar Explorer
 * iii – (s) Sichuan Yi language (ISO 639-2 code)
 * III – (s) Three (in Roman numerals)
 * IIMSS – If I May Say So
 * IIRC – If I Remember Correctly, If I Recall Correctly
 * IISS – (i) International Institute for Strategic Studies
 * IIT – (i) Illinois Institute of Technology – Indian Institutes of Technology – Indiana Institute of Technology
 * IITM – (i) Image Institute of Technology & Management – Indian Institute of Technology Madras – Indian Institute of Tropical Meteorology
 * I/ITSEC – (a) Interservice/Industry Training, Simulation and Education Conference ("eye-it-sec" or "it-sec")

IJ

 * IJN – (i) Imperial Japanese Navy (World War II)
 * IJWP – (i) Interim Joint Warfare Publication

IK

 * ik – (s) Inupiaq language (ISO 639-1 code)
 * IKEA – (a) Ingvar Kamprad (the company's founder), Elmtaryd (the farm where he was born and raised), Agunnaryd (a village and parish near the farm)
 * iku – (s) (s) Inuktitut language (ISO 639-2 code)

IM

 * IM
 * (s) Isle of Man (FIPS 10-4 territory code)
 * (i) Instant Message (Internet speech)
 * IMA
 * (i) Intermediate Maintenance Activity
 * Institute of Mathematics and Applications
 * – (i) International Migratory Bird Day
 * IMDb – Internet Movie Database
 * IME - (i) In My Experience
 * IMF
 * (i) id music file/id's music format (audio file format)
 * Impossible Missions Force, the protagonist organization in the Mission: Impossible media franchise
 * International Monetary Fund (the most common use for the initialism)
 * IMHO – (i) In My Humble/Honest Opinion, cf. IMO
 * IMIST AMBO – used to facilitate an informed clinical handover between paramedics, emergency department staff or other healthcare   similar to SBAR: Identification, Method of Injury, Index of concern, Signs, Treatment, Allergies, Medication, Background, and Other
 * IML – (i) International Mister Leather
 * IMLAST – (i) International Movement for Leisure Activities in Science and Technology – see MILSET
 * IMNM - (i) - Immune-mediated necrotizing myopathy a rare, but serious ADR of statins
 * IMNSHO – (i) In My Not So Humble Opinion
 * IMO (in my opinion) – (i) In My Opinion, also "imo", cf. IMHO
 * IMPAC – (a) International Merchant Purchase Authorization Card
 * IMPACT – (a) International Medical Products Anti-Counterfeiting Taskforce
 * IMPATT – (p) IMPact Avalanche Transit Time diode
 * IMPT – (i) Institute of Maxillofacial Prosthetists and Technologists
 * IMR – (i) Inzhenernaya Mashina Razgrazhdeniya (Russian Инженерные Машины Разграждения, "Engineer Vehicle Obstacle-Clearing") †
 * IMRI
 * (i) Industrial Membrane Research Institute
 * Information Management Research Institute
 * Institut pour le management de la recherche et de l'innovation (French, "Institute for the Management of Research and Innovation")
 * International Market Research Information
 * Intraoperative Magnetic Resonance Imaging
 * IMRO
 * Internal Macedonian Revolutionary Organization
 * Irish Music Rights Organisation
 * IMRL – (i) Individual Material Readiness List
 * IMS
 * (i) Information Management System
 * International Meat Secretariat
 * Ion Mobility Spectrometer
 * IMSA
 * (i) Illinois Mathematics and Science Academy
 * International Mind Sports Association
 * International Motor Sports Association
 * IMsL – (a) International Ms. Leather
 * IMT – (i) Integrated Management Tool
 * IMU – (i) International Mathematical Union

IN

 * In – (s) Indium
 * IN – (s) India (FIPS 10-4 country code; ISO 3166 digram) – Indiana (postal symbol) – Infantry
 * ina – (s) Interlingua language (ISO 639-2 code)
 * INA – (p) Immigration and Nationality Act
 * INAS – (a) International Near-Earth Asteroid Survey
 * INC – (i) Indian National Congress, one of the national political parties in India
 * (i) Iglesia ni Cristo (Filipino, "Church of Christ")
 * Indian National Congress
 * International Network of Crackers
 * Iraqi National Congress
 * INCITS – (p) InterNational Committee for Information Technology Standards
 * ind – (s) Indonesian language (ISO 639-2 code)
 * IND – (s) India (ISO 3166 trigram)
 * inet – (a) the Internet
 * INDIGO – (p) (U.S.) INtelligence DIvision Gaming Operation
 * INFORMS – (a) (U.S.) Institute for Operations Research and the Management Sciences
 * INFOSEC – (p) Information Security
 * INLA – (i) Irish National Liberation Army
 * INMARSAT – (p) International Maritime Satellite organization
 * INR – (s) Indian rupee (ISO 4217 currency code)
 * INRI – (a/i) Iesus Nazarenus Rex Iudæorum (Latin, "Jesus of Nazareth, King of the Jews")
 * INRIA – (p) Institut national de recherche en informatique et en automatique
 * INS – (i) Immigration and Naturalization Service
 * InSAR – (p) Interferometric synthetic aperture radar
 * INST – (p) Information Standards and Technology
 * in trans. – (p) in transitu (Latin, "in transit")
 * INTSUM – (p) Intelligence Summary
 * INTERFET – (p) International Force for East Timor

IO

 * io – (s) Ido language (ISO 639-1 code)
 * IO – (s) British Indian Ocean Territory (ISO 3166 digram; FIPS 10-4 territory code)
 * IOC
 * (i) Initial Operational Capability
 * Intergovernmental Oceanic Commission
 * International Olympic Committee
 * International Ornithological Congress
 * IOG (formerly IOHK) – Input Output Global. Redirected to Charles Hoskinson
 * IOHK – Input Output Hong Kong. Redirected to Charles Hoskinson
 * IOLTA – (a) Interest on Lawyer Trust Accounts (charitable funding mechanism, especially for legal aid)
 * IOM
 * (i) Iowa, Ohio, Michigan (soybean origin)
 * Institute of Medicine
 * International Organisation for Migration
 * Isle of Man
 * IONA – (i) Islands of the North Atlantic (alternate name for Great Britain, Ireland, the Isle of Man, and related islands)
 * IoT - (i) Internet of Things
 * IOT – (s) British Indian Ocean Territory (ISO 3166 trigram)
 * IOT&E – (i) Initial Operational Test and Evaluation
 * IOU – (p) "I Owe You" (Promissory note)

IP

 * IP –
 * (s) Clipperton Island (FIPS 10-4 territory code)
 * (i) Initial Point – Intellectual Property – Internet Protocol
 * IPA – (i) India Pale Ale – International Phonetic Alphabet – Isopropyl alcohol
 * IPB – (i) Intelligence Preparation of the Battlefield
 * IPCC –
 * (i) Intergovernmental Panel on Climate Change
 * Independent Police Complaints Commission
 * ipk – (s) Inupiaq language (ISO 639-2 code)
 * IPL – (i) Inferior Parietal Lobule
 * IPN – (i) Instytut Pamieci Narodowej (Polish, "Institute for National Memory")
 * IPO – (i) Initial public offering
 * IPR –
 * (i) In Progress Review
 * Intellectual Property Rights
 * Intelligence Production Requirement
 * IPT – (i) Integrated Product/Project Team
 * IPTS – (i) Institute for Prospective Technological Studies
 * IPTV – (p) Internet Protocol TeleVision
 * IPW – (i) Interrogation of Prisoners of War

IQ

 * iq – (i) idem quod (Latin, "the same as")
 * IQ –
 * (i) Intelligence Quotient
 * (s) Iraq (ISO 3166 digram)
 * IQD – (s) Iraqi dinar (ISO 4217 currency code)

IR

 * Ir – (s) Iridium
 * IR
 * (i) Infrared
 * Intelligence requirement (military)
 * (s) Iran (FIPS 10-4 country code; ISO 3166 digram)
 * Iran Air (IATA alpha code) see entry for more
 * IRA
 * (i) Individual retirement account
 * (i) Irish Republican Army (any of several armed groups dedicated to Irish republicanism)
 * Internet Research Agency (used in the Mueller report)
 * IRAD – (a) Internal Research and Development
 * IRAN - (I) Inspect and Repair As Necessary
 * IRAS – (p) Infrared Astronomical Satellite
 * IRB – (i) International Rugby Board, a former name of World Rugby
 * IRBM – (i) Intermediate Range Ballistic Missile
 * IRC
 * (i) International Red Cross
 * International reply coupon
 * (i) Internet Relay Chat
 * IREA
 * (i) Intermountain Rural Electric Association
 * (i) International Renewable Energy Alliance
 * (p) Iranian Esperanto Association
 * (i) Internet Radio Equality Act
 * IRGC - (i) Islamic Revolutionary Guard Corps (branch of Iranian Armed Forces
 * IRL
 * (s) Ireland (ISO 3166 trigram)
 * Industrial Research Limited
 * Indy Racing League, former name of the motorsport governing body now known as INDYCAR
 * (i) In real life
 * IRM
 * (i) Illinois Railway Museum
 * Inzhenernaya Razvedyvatelnaya Mashina (Russian Инженерная Разведывательная Машина, "Engineer Reconnaissance Vehicle") †
 * IRN – (s) Iran (ISO 3166 trigram)
 * IRIAF - Islamic Republic of Iran Air Force
 * IRINN - Islamic Republic of Iran News Network
 * IRO – (i) International Refugee Organisation
 * IRQ – (s) Iraq (ISO 3166 trigram)
 * IRR – (s) Iranian rial (ISO 4217 currency code)
 * IRS – (i) U.S. Internal Revenue Service
 * IRSN – (i) Institut de radioprotection et de sûreté nucléaire (French, "Institute for Radiation Protection and Nuclear Safety")
 * IRST – (i) Infra-red Search and Track

IS

 * is – (s) Icelandic language (ISO 639-1 code)
 * IS
 * (s) Iceland (ISO 3166 digram)
 * Israel (FIPS 10-4 country code)
 * ISA
 * (i) Individual Savings Account
 * Industry Standard Architecture
 * Instruction Set Architecture
 * International Seabed Authority
 * ISAAA – (i) International Service for the Acquisition of Agri-biotech Applications
 * ISAF
 * (a) International Sailing Federation
 * International Security Assistance Force
 * ISAR – (a) Inverse SAR (Synthetic Aperture Radar)
 * ISB – (i) Intermediate Staging Base
 * ISBN – (i) International Standard Book Number (ISO 2108)
 * ISCCP – (i) International Satellite Cloud Climatology Project
 * ISCII – (a) Indian Standard Code for Information Interchange
 * ISDN – Integrated Services Digital Network
 * ISEF – (a) Intel International Science and Engineering Fair
 * ISEN – (i) Internet Search Environment Number
 * ISF – (i) Internal Security Force
 * ISI
 * Indian Standards Institute, former name of the Bureau of Indian Standards
 * Inter-Services Intelligence (Pakistan)
 * Islamic State of Iraq, an umbrella organization for several Iraqi insurgent groups
 * ISIL – (i/a) Islamic State of Iraq and the Levant
 * ISIS
 * (i/a) Institute for Science and International Security
 * Islamic State of Iraq and Syria
 * ISK – (s) Icelandic krona (ISO 4217 currency code)
 * isl – (s) Icelandic language (ISO 639-2 code)
 * ISL – (s) Iceland (ISO 3166 trigram)
 * ISLN –
 * (i) International Standard Lawyer Number (used initially by LexisNexis Martindale-Hubbell)
 * (i) International School Libraries Network (HQ in Singapore)
 * (s) Isilon Systems, the NASDAQ symbol
 * ISM
 * (i) Industrial, scientific or medical
 * (p) Interstellar medium
 * ISMB – (i) International Society of Matrix Biologists
 * ISMC – (i) Intelligent Sounding Meaningless Conversation
 * ISO
 * (i) In Search Of
 * (s) International Organization for Standardization (from the Greek ίσος, isos, meaning "equal")
 * ISOGP – (i) Indian Society of Orthodontics for General Practitioners
 * ISP
 * (i) International Standardized Profile
 * Internet Service Provider
 * Information Systems Professional
 * ISPE – (a/i) International Society for Pharmacoepidemiology
 * ISR
 * (i) Intelligence, Surveillance and Reconnaissance
 * (s) Israel (ISO 3166 trigram)
 * ISRO – (i) Indian Space Research Organisation
 * ISS
 * (i) International Shorebird Survey (North America)
 * International Space Station
 * ISSCR – (i) International Society for Stem Cell Research
 * ISSN – (i) International standard serial number (ISO 3297)
 * IST
 * (i) Information System Technology
 * UCF Institute for Simulation and Training
 * ISTAR – (i) Intelligence, Surveillance, Target Acquisition, and Reconnaissance
 * ISTC – (i) Institute of Scientific and Technical Communications (UK)
 * ISTG – (i) I Swear To God
 * ISTS – (i) Intel Science Talent Search
 * ISU
 * (i) Integrated Sight Unit
 * International Skating Union

IT

 * it – (s) Italian language (ISO 639-1 code)
 * IT
 * (i) InferoTemporal (neurophysiology)
 * Information Technology
 * (s) Italy (FIPS 10-4 country code; ISO 3166 digram)
 * ita – (s) Italian language (ISO 639-2 code)
 * ITA – (s) Italy (ISO 3166 trigram)
 * ITAG – (i) Inertial Terrain-Aided Guidance
 * ITALY – (a) I'll Truly Always Love You
 * ITAS – (i) Improved Target Acquisition Sight
 * ITC
 * (i) Incorporated Television Company (defunct British television production company)
 * InferoTemporal Cortex (neurophysiology)
 * ITCZ – (i/p) Intertropical Convergence Zone
 * ITEC – (a) Information Technology Exposition & Conference
 * ITEMS – (a) Interactive Tactical Environment Management System
 * ITER – (a) International Thermonuclear Experimental Reactor
 * ITF – (a) International Tennis Federation
 * ITK – (a) In The Know
 * ITN – (i) Independent Television News (British)
 * ITS
 * (i) Incompatible Time-sharing System
 * Individual Training Standards
 * ITT – (i) International Telephone and Telegraph (U.S.)
 * ITTO – (i) International Tropical Timber Organization
 * ITU
 * (i) Intent-to-Use
 * International Telecommunication Union (International Telegraph Union 1865–1932)

IU

 * iu – (s) (s) Inuktitut language (ISO 639-1 code)
 * IUCN – (i) International Union for the Conservation of Nature and Natural Resources (World Conservation Union)
 * IUD – (i) Intrauterine device (https://www.plannedparenthood.org/learn/birth-control/iud)
 * IUI
 * (i) Indiana University Indianapolis, to be established in 2024 upon the dissolution of Indiana University–Purdue University Indianapolis (IUPUI, below)
 * Intrauterine insemination (http://americanpregnancy.org/infertility/intrauterine-insemination/)
 * IUPAC – (a) International Union of Pure and Applied Chemistry (pronounced "eye-yoo-pac")
 * IUPUI – (a) Indiana University–Purdue University Indianapolis
 * IUSS
 * (i) Integrated Undersea Surveillance System
 * Integrated Unit Simulation System
 * International Union of Soil Sciences

IV

 * IV – (s) Côte d'Ivoire (FIPS 10-4 country code; from Ivory Coast) – Four (in Roman numerals) – (i) IntraVenous (as in intravenous drip or intravenous therapy)
 * IVD – (i) Internet Video Device, intra vas device
 * Iveco – (p) Industrial Vehicles Corporation
 * IVF – (i) In Vitro Fertilisation
 * IVI – (i) Interchangeable Virtual Instrument
 * IVIS – (i/a) Inter-Vehicle Information System
 * IVL – (i) Inter-Visibility Line
 * IVM – (i) In Vitro [Oocyte] Maturation
 * IVO – (i) In Vicinity Of

IW

 * IW – (i) Impact Wrestling
 * IW – (i) Information Warfare
 * IWARS – (p) Infantry Warrior Simulation
 * IWC – (i) International Whaling Commission
 * IWT – (i) Illegal Wildlife Trade
 * IWW – (i) Industrial Workers of the World

IX

 * IX – (s) Nine (in Roman numerals)

IY

 * IY – (s) Saudi–Iraqi neutral zone (FIPS 10-4 territory code; obsolete 1993)
 * Iykyk (acronym) – (i) If You Know You Know

IZ

 * IZ – (s) Iraq (FIPS 10-4 country code)