| IRTC | International Rehabilitation Council for Torture | In English | → Fundamental rights |
| IS | Internacia Seminario | In Esperanto | → Congresses |
| ISA | International Seabed Authority (www.isa.org.jm) | In English | → International relations → Marine research, oceanography → Mining |
| ISA | International Sociological Association | In English | → Associations → Sociology |
| ISAE | Internacia Scienca Asocio Esperantista | In Esperanto | → Associations → Mathematics and natural sciences |
| ISAFIS | Indonesian Student Association for International Studies | In English | → Associations → Higher education, universities |
| ISAZ | International Society for Anthrozoology | In English | → Zoology |
| ISBL | Institution(s) sans but lucratif | In French | |
| ISBS | Internationales Symposium für Biomechanik im Sport | In German | → Congresses → Biological sciences → Sport, physical exercises |
| ISC | International Seismological Centre (www.isc.ac.uk) | In English | → Research institutes → Seismology, earthquakes |
| ISC | Ingense Sport Club | In Dutch | → Sport, physical exercises |
| ISCAR | International Society for Cultural and Activity Research | In English | → Social sciences → Civilization, culture, progress |
| ISCOS | Istituto Sindacale per la Cooperazione allo Sviluppo | In Italian | → Development |
| ISD | International Society of Differentiation | In English | → Biological sciences |
| ISDP | International Society for Developmental Psychobiology (www.isdp.org) | In English | → Developmental psychology → Biological sciences |
| ISDP | Institute for Security & Development Policy (www.isdp.eu) | In English | → Research institutes → Politics → Development |
| ISDP | International Society of Dermatopathology | In English | → Dermatology |
| ISE | Internacia Semajnfino Esperantista | In Esperanto | → Congresses |
| ISE | Institut Syndical Européen | In French | → Labour, labour economics |
| ISEGI | Instituto Superior de Estatística e Gestão de Informação | In Portuguese | → Research institutes → Statistics |
| ISEM | Institut des Sciences de l'Évolution de Montpellier | In French | → Research institutes → Biological sciences |
| ISER | Institute for Social and Economic Research | In English | → Research institutes → Demography, statistics, sociology → Economics |
| ISF | Ingénieurs Sans Frontières | In French | → Engineering, technology |
| ISFP | International Society for Fibrinolysis and Proteolysis | In English | → Biochemistry, biophysics |
| ISHEASTM | International Society for the History of East Asian Science Technology and Medicine | In English | → History → Medicine → Engineering, technology |
| ISHS | International Society for Horticultural Science | In English | → Horticulture |
| ISI | Integral Satcom Initiative (www.isi-initiative.eu.org) | In English | → 645 → Spaceflight engineering, astronautics |
| ISIAO | Istituto italiano per l'Africa e l'Oriente | In Italian | |
| ISIR | Institut des Systèmes Intelligents et de Robotique | In French | → Research institutes → Artificial intelligence → Electrical engineering → Engineering, technology |
| ISIR | Institut für Statistik und internationale Registrierungen | In German | → Research institutes → Statistics |
| ISIR | International Society for Intelligence Research | In English | → Neurology |
| ISIR | Institut des Systèmes Intelligents et Robotique | In French | → Research institutes → Mechanical engineering → Electronics |
| ISIR | International Society for Interferon-Research | In English | → Biochemistry, biophysics → Medicine |
| ISIR | International Society for Immunology of Reproduction | In English | → Immunology and allergy → Reproductive biology |
| ISIS | International Society of Infant Studies | In English | → Education → Pediatry |
| ISL | Inertial Systems Laboratory | In English | → Research institutes → Mechanical engineering |
| ISM | Institut des Sciences Moléculaires | In French | → Research institutes → Biochemistry, biophysics |
| ISME | International Symposium on Microbial Ecology | In English | → Congresses → Ecology |
| ISME | Irish Small and Medium Enterprises | In English | → Economic policy |
| ISO | International Standardization Organization | In English | → Standardization |
| ISOC | Internet Society | In English | → Internet |
| ISOPT | International Symposium on Ocular Pharmacology and Therapeutics | In English | → Congresses → Pharmacology, toxicology → Ophtalmology |
| ISP | Instytut Studiów Politycznych | In Polish | → Research institutes → Politics |
| ISPG | International Society of Psychiatric Genetics | In English | → Genetics → Psychiatry |
| ISPOG | International Society of Psychosomatic Obstetrics and Gynecology | In English | → Psychology → Gynaecology → Obstetrics |
| ISR | Instituto de Sistemas e Robótica | In Portuguese | → Research institutes → Electrical engineering |
| ISRA | Islamic Research Academy | In English | → Academies → Islam |
| ISS | Institute of Social Studies | In English | → Sociology |
| ISSBD | International Society for the Study of Behavioral Development | In English | → Developmental psychology |
| ISSIR | International Society for Sexual and Impotence Research | In English | → Sexual problems → Urology → Applied sciences, technology |
| ISSM | International Society for Sexual Medicine | In English | → Urology → Gynaecology → Psychology |
| ISST | International Society of Seed Technologists | In English | → Agricultural sciences |
| ISST | International Society for the Study of Time | In English | |
| ISST | International Ski & Sun Team | In English | → 786 |
| ISSTD | International Society for the Study of Trauma and Dissociation | In English | → Neurology |
| IST | Istituto Scientifico Tumori | In Italian | → Research institutes → Oncology |
| ISTA | International Seed Testing Association | In English | → Associations → Agricultural sciences |
| ISTAG | Information Society Technologies Advisory Group | In English | → Networks, communication → Telecommunications |
| ISTH | International Society on Thrombosis and Haemostasis | In English | → Cardiology |
| ISUOG | International Society of Ultrasound in Obstetrics and Gynecology (www.isuog.org) | In English | → Diagnostics → Gynaecology, obstetrics |
| ISV | Institut des Sciences du Végétal | In French | → Research institutes → Biological sciences → Botany |
| ISV | Institut des Sciences de la Vision (www.isvision.fr) | In French | → Ophtalmology |
| ISVMA | Illinois State Veterinary Medical Association (www.isvma.org) | In English | → Associations → Veterinary medicine |
| ITAA | Information Technology Association of America | In English | → Associations → Computer science → Telecommunications |
| ITASEAS | Italian Association for Southeast Asian Studies | In English | → Associations → Area studies |
| ITI | Instituto Tecnológico de Informática (www.iti.upv.es) | In Spanish | → Research institutes → Computer science |
| ITO | International Trade Organization | In English | → Trade → International economic cooperation |
| ITQB | Instituto de Tecnologia Química e Biológica | In Portuguese | → Research institutes → Biological sciences → Chemical technology |
| ITRE | Internacia Traduk-Reto per Esperanto | In Esperanto | → Artificial languages (linguistics) |
| ITS | International Tracing Service (http://its-arolsen.org) | In English | |
| ITSC | Interregional Telecommunications Standards Committee | In English | → Networks, communication → Telecommunications |
| ITSTC | Information Technology Steering Committee | In English | → Computer science → Telecommunications |
| ITTO | International Tropical Timber Organization (www.itto.or.jp) = OIBT | Organisation Internationale des Bois Tropicaux | In French = OIMT | Organización Internacional de las Maderas Tropicales | In Spanish |
In English | → Nature and society → Timber and woodworking industry |
| ITU | International Telecommunication Union = IUT | Internacia Unio pri Telekomunikado | In Esperanto = UIT | Union Internationale des Télécommunications | In French |
In English | → Telecommunications |
| ITU | Institut für Transurane | In German | → Research institutes → Nuclear, atomic, and molecular physics → Nuclear technology |
| ITUC | Interregional Trade Union Council | In English | → Labour, labour economics |
| ITUH | International Trade Union House | In English | → Labour, labour economics |
| IUCr | International Union of Crystallography (www.iucr.org) | In English | → Crystallography |
| IULO | International Union of Local Authorities | In English | → Municipal administration |
| IUOTO | International Union of Official Travel Organisations | In English | → Tourism |
| IUOTPO | International Union of Official Tourist Publicity Organizations | In English | → Tourism |
| IUPAC | International Union of Pure and Applied Chemistry | In English | → Chemistry → Chemical technology |
| IUPAK | Internacia Unio pri Pura kaj Aplika Kemio |
In Esperanto | → Chemistry → Chemical technology |
| IUPRAI | Indian Unit for Pattern Recognition and Artificial Intelligence | In English | → Artificial intelligence → Computer-based techniques |
| IUT | Internacia Unio pri Telekomunikado = ITU, UIT (look above) |
In Esperanto | → Telecommunications |
| IV | Industriellenvereinigung (www.iv-net.at) | In German | → Industry, industrial policy |
| IVA | Indian Vexillological Association | In English | → Associations → 9299 |
| IVG | Internationale Vereinigung für Germanistik | In German | → Language, linguistics, literature |
| IVK | Institut für Verbrennungskraftmaschinen und Kraftfahrzeugbau (www.ivk.tuwien.ac.at) | In German | → Research institutes → Mechanical engineering → Vehicle engineering |
| IVMA | Indiana Veterinary Medical Association (www.invma.org) | In English | → Associations → Veterinary medicine |
| IVO | Inspanning Voor Ontspanning | In Dutch | → Sport, physical exercises |
| IVS | In Vriendschap Sterk | In Dutch | → Sport, physical exercises |
| IVS | Institut des Vaisseaux et du Sang (www.ivs-vbi.org) = VBI | Vessels and Blood Institute | In English |
In French | → Research institutes → Blood and circulatory system |
| IVS | Irish Veterinary Association | In English | → Associations → Veterinary medicine |
| IVSA | International Veterinary Students Association (www.ivsa.org) | In English | → Associations → Higher education, universities → Veterinary medicine |
| IVV | Ilper Voetbal Vereniging | In Dutch | → Sport, physical exercises |
| IWA | International Water Association | In English | → Associations → Hydrology → Environmental technology, water supply, waste management |
| IWC | International Whaling Commission | In English | → International relations → Fishing, hunting |
| IWEPNM | International Winterschool on Electronic Properties of Novel Materials | In English | → Congresses → Physics → Chemistry |
| IWF | Institut für Weltraumforschung (www.iwf.oeaw.ac.at) | In German | → Research institutes → Astronomy → Spaceflight engineering, astronautics |
| IWF | International Weightlifting Federation (www.iwf.net) | In English | → Sport, physical exercises |
| IWFHR | International Workshop on Frontiers in Handwriting Recognition | In English | → Congresses → Writing systems → Document processing |
| IWI | Industriewissenschaftliches Institut | In German | → Research institutes → Industry, industrial policy → Engineering, technology |
| IWM | Institut für die Wissenschaften vom Menschen (www.iwm.at) | In German | → Research institutes → Social sciences |
| IWRS | International Wheelchair Rugby Federation | In English | → Football and rugby |
| IWTO | International Wool Textile Organization | In English | → Textile industry |
| IYS | Igud Yotzei Sin | In Chinese | → Judaism |
| IZT | Institut für Zukunftsstudien und Technologiebewertung (www.izt.de) | In German | → Research institutes → Research policy → Engineering, technology |
| JABS | Justice Awareness and Basic Support | In English | → Law, jurisprudence → Pharmacology, toxicology |
| JAEL | JSC (Johnson Space Center) Avionics Engineering Laboratory | In English | → Research institutes → Aeronautics, aircraft |
| JAFS | Japan Asian Association and Asian Friendship Society | In English | → Associations → International relations |
| JAICI | Japan Association for International Chemical Information | In English | → Associations → Chemistry |
| JALAM | Japanese Association for Laboratory Animal Medicine | In English | → Associations → Medicine |
| JALT | Japan Association for Language Teaching | In English | → Associations → Education → Linguistics |
| JAM | Junulara Azia Movado | In Esperanto | |
| JAMI | Jewish Association for the Mentally Ill | In English | → Associations → 61889 |
| JAMS | Japanese Association for Mathematical Sociology | In English | → Associations → Sociology |
| JARI | Japan Automobile Research Institute | In English | → Research institutes → Automobile manufacturing → Transport and postal services |
| JASAS | Japanese Association for South Asian Studies | In English | → Associations → Area studies |
| JASRAC | Japanese Society for Rights of Authors | In English | → Artistic property |
| JAVA | Japanese Vexillological Association | In English | → Associations → 9299 |
| JBLE | Japana Budhana Ligo Esperantista | In Esperanto | → Buddhism |
| JbRGZM | Jahrbuch des römisch-germanische Zentralmuseen | In German | → Serial publications, periodicals → Museums |
| JCC | Jewish Community Center | In English | → Judaism |
| JCIE | Japan Center for International Exchange (www.jcie.or.jp) | In English | → International relations |
| JCLTA | Journal of the Chinese Language Teachers Association | In English | → Associations → Linguistics |
| JEA | Jordan Engineers Association = JEA | نقابة المهندسين الأردنيين | In Arabic |
In English | → Associations → Engineering, technology |
| JEA | Journalism Education Association | In English | → Associations → Newspapers, journalism → Education |
| JEA | نقابة المهندسين الأردنيين = (look above) |
In Arabic | → Engineering, technology |
| JEA | Junularo Esperantista Apula | In Esperanto | |
| JEB | Junaj Esperantistoj en Britio (www.novajeb.org.uk) | In Esperanto | |
| JEB | Junularo Esperantista Brita (www.novajeb.org.uk) | In Esperanto | → Associations |
| JEF | Japan Economic Foundation | In English | → Foundations → Economics |
| JEFO | Junulara Esperantista Franca Organizo | In Esperanto | |
| JEI | Japana Esperanto-Instituto | In Esperanto | |
| JEIDA | Japan Electronic Industry Development Association | In English | → Associations → Electronics |
| JEJ | 日本青年エスペラント連絡会 = JEJ | Japana Esperanto-Junularo | In Esperanto |
In Japanese | |
| JEJ | Japana Esperanto-Junularo = (look above) |
In Esperanto | |
| JEK | Junularo Esperantista Kanada | In Esperanto | |
| JEKA | Jeugdig Enthousiasme Kan Alles | In Dutch | |
| JELI | Junulara Esperanto-Ligo Israela | In Esperanto | |
| JEP | Jeunes Européens - Professionnels | In English | |
| JES | Junularo Esperantista Svislanda (www.jesperanto.ch) | In Esperanto | → Associations |
| JFA | Jeropeeske Frijhannelsassosjaasje (www.efta.int) = EFTA | European Free Trade Association | In English = ESVO | Evropské sdružení volného obchodu | In Czech = AELE | Association Européenne de Libre-Échange | In French = EMAE | Europako Merkataritza Askearen Elkartea | In Basque = AELE | Associacion eropèèna de libro-èchanjo | In Franco-Provençal = AELC | Asociación Europea de Libre Comercio | In Spanish = ELKA | Eŭropa Liber-Komerca Asocio | In Esperanto = EFTA | 欧洲自由贸易联盟 | In Chinese = EVA | Europese Vrijhandelsassociatie | In Dutch = AELE | Associacion Europèa de Liure Escambi | In Occitan = ЕСТА | Европска Слободна Трговска Асоцијација | In Macedonian = AELS | Asociaţia Europeană a Liberului Schimb | In Romanian = ЄАВТ | Європейська асоціація вільної торгівлі | In Ukrainian = ЕФТА | Европска слободна трговинска асоцијација | In Serbian = EZVO | Európske združenie voľného obchodu | In Slovak = ЕАСТ | Европейская ассоциация свободной торговли | In Russian |
In Frisian | → Associations → Trade |
| JHK | Jan Hanzen Kwartier | In Dutch | → Sport, physical exercises |
| JILA | Joint Institute for Laboratory Astrophysics (http://jilawww.colorado.edu) | In English | → Research institutes → Astronomy |
| JISC | Joint Information Systems Committee | In English | → Libraries |
| JK | Japana Kongreso | In Esperanto | → Congresses |
| JMA | Juna Membro-Abonanto | In Esperanto | → Newspapers, journalism |
| JMJ | Juna Membro kun Jarlibro | In Esperanto | |
| JOS | Jeugd Organisatie Sportclub | In Dutch | → Sport, physical exercises |
| JOTE | Junulara Organizo de Togolandaj Esperantistoj | In Esperanto | |
| JPEG | Joint Photographic Experts Group | In English | → Graphical processing → Image processing |
| JPG | Joint Presidents Group | In English | |
| JPL | Jet Propulsion Laboratory | In English | → Research institutes → Spaceflight engineering, astronautics |
| JPS | Jonge Protestanten die Samenwerken | In Dutch | → Protestant churches |
| JPS | Jean Piaget Society | In English | → Developmental psychology |
| JSA | Japanese Standards Association | In English | → Standardization → Associations |
| JSAA | Japan Studies Association of Australia | In English | → Associations → Language, linguistics, literature → Geography, biography, history |
| JSAC | Japan Studies Association of Canada | In English | → Associations → Language, linguistics, literature → Geography, biography, history |
| JSASS | Japan Society of Aeronautical Space Sciences | In English | → Aeronautics, aircraft → Spaceflight engineering, astronautics |
| JSES | Japan Society of Educational Sociology | In English | → Sociology |
| JSK | Jeunesse Sportive de Kabylie | In French | → Sport, physical exercises |
| JSLAE | Japanese Society for Laboratory Animal and Environment | In English | → Medicine → Veterinary medicine |
| JSMA | Japan Society of Microgravity Application | In English | → Physics |
| JSMB | Japanese Society for Mathematical Biology | In English | → Mathematics → Biological sciences |
| JSOG | Japanese Society of Obstetrics and Gynecology | In English | → Gynaecology → Obstetrics |
| JSPS | Japan Society of Promotion Science | In English | → Science and knowledge |
| JSV | Jutphaasse Sport Vereniging | In Dutch | → Sport, physical exercises |
| JSVS | Japanese Society of Veterinary Science | In English | → Veterinary medicine |
| JTC | Joint Technical Committee | In English | → Engineering, technology |
| JVA | Jan Van Arckel | In Dutch | → Sport, physical exercises |
| JVC | Julianadorper Voetbal Club | In Dutch | → Football and rugby |
| JVC | Jan Van Cuijk | In Dutch | → Sport, physical exercises |
| JVV | Jipsingbourtangense Voetbal Vereniging | In Dutch | → Sport, physical exercises |
| JWG | Joint Working Group | In English | |
| KA | Kirkelig arbeidsgiver- og interesseorganisasjon | In Norwegian | → Labour, labour economics → Christianity |
| KA | Knattspyrnufélag Akureyrar (www.ka-sport.is) | In Icelandic | → Sport, physical exercises |
| KAEM | Komisiono pri Azia Esperanto-Movado | In Esperanto | |
| KAERI | Korea Atomic Energy Research Institute (www.kaeri.re.kr) | In English | → Research institutes → Atomic physics |
| KAEST | Konferenco pri Aplikoj de Esperanto en Scienco kaj Tekniko | In Esperanto | → Congresses → Mathematics and natural sciences → Applied sciences, technology |
| KAF | Korean-American Forum | In English | |
| KAM | Kansas Association of Mappers (www.kam.to) | In English | → Associations → 332 |
| KAÖ | Katholische Aktion Österreich | In German | → Roman catholic church |
| KarEsA | Kartvelia Esperanto-Asocio | In Esperanto | → Associations |
| KBV | Kampioen Bij Volharding | In Dutch | → Sport, physical exercises |
| KCAA | Kansas County Appraisers Association (www.accesskansas.org/kcaa) | In English | → Associations → 332 |
| KDC | Koolhazen Dochteren Combinatie | In Dutch | → Sport, physical exercises |
| KDO | Kracht Door Oefening | In Dutch | → Sport, physical exercises |
| KDPS | (The) Kanji Dictionary Publishing Society | In English | → Dictionaries → Language, linguistics, literature → Graphic industries, printing, publishing |
| KDS | Kracht Door Samenwerking | In Dutch | → Sport, physical exercises |
| KEA | Kanada Esperanto-Asocio | In Esperanto | → Associations |
| KEA | Kataluna Esperanto-Asocio | In Esperanto | → Associations |
| KEA | Kuba Esperanto-Asocio | In Esperanto | → Associations |
| KEILEU | Komitato por la Enkonduko de la Internacia Lingvo en Eŭropan Union | In Esperanto | → International relations → Language, linguistics, literature |
| KEJ | Kataluna Esperanto-Junularo (www.esperanto.cat/kej/) | In Esperanto | |
| KEJ | 韓国における青年エスペラント団体です |
In Japanese | |
| KEJ | Korea Esperanto-Junularo | In Esperanto | |
| KEJA | Kroata Esperanto-Junulara Asocio (www.keja.hr) = HEM | Hrvatska Esperantska Mladež | In Croatian |
In Esperanto | → Associations |
| KEJO | Kebekia Esperantista Junulara Organizo | In Esperanto |
|