| Abbreviation | Definition |
|---|---|
| IRO | International Refugee Organization (WWII) |
| IRO | International Relief Organization |
| IRS | International Relief Service |
| IS | Intermediate State (in the Theory of Change) |
| ISA | International Seabed Authority |
| ISC | Inter Sector Coordinator |
| ISCE | International Standard Classification Education |
| ISCG | Inter-Sector Coordination Group |
| ISDB | Islamic Development Bank |
| ISDR | International Strategy for Disaster Reduction |
| ISKO | International Society for Knowledge Organization |
| ISM | International Solidarity Movement |
| ITC | International Trade Centre |
| ITLOS | International Tribunal for the Law of the Sea |
| ITO | International Trade Organization |
| ITPGRFA | International Treaty on Plant Genetic Resources for Food and Agriculture Resources |
| ITU | International Telecommunication Union |
| ITU | nternational Telecommunication Union |
| IULA | International Union of Local Authorities |
| IULA | nternational Union of Local Authorities |