| Instructional Resource and Technology Center | Academic & Science |
| Industrial Refrigeration Technical College | Academic & Science |
| Integrated Research and Training Center | Academic & Science |
| Intuitive Research and Technology Corporation | Academic & Science |
| Institute of Robotics and Technical Cybernetics | Academic & Science |
| Incheon Rapid Transit Corporation | Business |
| Investment Recovery Trade Corporation | Business |
| Internet Resources for Technical Communicators | Community |
| International Rolling Technology Course | Community |
| Indonesian RC Tank Community | Community |
| Institute for Religion, Technology, and Culture | Community |
| Intensive Residential Treatment Center | Community |
| Integrated Rural Technology Centre | Computing |
| Instructional Resource Technology Center | Computing |
| Illinois Rural TeleCommunication in Computing | Computing |
| Internet Raytracing Competition | Computing |
| Integrated Resource Timber Contract | General |
| Internationally Recommended Transit Corridor | General |
| Institutional Reconciliation and Transformation Commission | General |
| Independent Rough Terrain Center | General |
| Independent Radio and Television Commission | General |
| Infantry Replacement Training Center | General |
| Immaterial Replacement Training Center | General |
| Inter Regularity Time Control | General |
| Indianapolis Regional Transportation Council | Governmental |
| Interlake Reserves Tribal Council | Governmental |
| International Research Terms and Conditions | International |
| International Recommended Transit Corridor | International |
| Intestinal Rehabilitation and Transplantation Center | Medical |
| International Research and Training Center | Military and Defence |
| Illinois Rural Telecommunication | Telecommunication |
