| OY | Omni Air International [IATA-Airline-Code/ USA] |
| OPAL | Omni-Purpose Apparatus at LEP |
| VOR | Visual Omni-Range |
| BOOM | Binary Omni-Oriented Monitor [engl.] |
| OC | OMNI Aviaçao & Teconologia [IATA-Airline-Code/ Portugal] |
| int. | international [dt.] |
| GNI | GayNet International |
| IS | International Standard [ISO] |
| is | International Standard |
| iX | International Exchanges |
| KI | Kiwanis International |
| Environ. Int. | Environment International Zeitschrift |
| IXI | International X.25 Interconnect |
| IAD | Dulles International Washington DC |
| IU | International Unit |
| NI 200 | DMV International GmbH Nörten-Hardenberg, Niedersachsen |
| IES | International EPR Society |
| INC | International Carrier |
| TI | Transparency International e.V. Berlin, http://www.transparency.de |
| IA | International Alphabet |
| INN | International Non-proprietary Name |
| intl. | international [engl.] |
| UI | Unix International |
| INTA | International Trademark Association |
| IIHF | International Ice Hockey Federation |
| IHT | International Herald Tribune |
| IHOP | International House Of Pancakes Glendale, http://www.ihop.com |
| INTERFUND | International Monetary Fund vgl. IWF |
| INET | International Networking Conference |
| IOC | International Operating Center |
| IHA | International Hotel Association |
| IGY | International Geophysical Year |
| IGM | International Golf Maintenance |
| IMDb | International Movie Database |
| IMF | International Monetary Fund Internationaler Währungsfonds [IWF] |
| INAC | International Network of Associated Consultants http://www.inac-global.com |
| INAC | INTERNATIONAL NETWORK OF ACTORS Berlin, http://www.inac-berlin.de |
| INN | International Network News |
| IMT | International Mobile Telecommunications |
| Int. J. Climatol. | International Journal of Climatology Zeitschrift |
| Int. Lichenol. Newsl. | International Lichenological Newsletter Zeitschrift |
| IMU | International Mathematical Union |
| Int. Peat J. | International Peat Journal Zeitschrift |
| IMS | International Monitoring System |
| IMO | International Maritime Organization Internationale Seeschiffahrtsorganisation |
| IGM | International Graphic Machinery Boom, [BE], http://www.igm-machinery.be |
| IFR | International Financial Review |
| ICL | International Computers Limited |
| ICJ | International Court of Justice |
| ICHO | International Chemistry Olympiad Kiel, http://www.icho.de |