| Abbreviation | Definition |
|---|---|
| IMS | Interstate Milk Shippers |
| IMSA | Insurance Marketplace Standards Association |
| IMSA | International Medical Students Association |
| IMSA | International Memorialization Supply Association |
| IMSA | International Motor Sports Association |
| IMSA | International Municipal Signal Association |
| IMSS | International Mass Spectrometry Society |
| IMTA | Irish Massage Therapists' Association |
| IMU | International Mathematical Union |
| INA | International Networking Association |
| INANE | International Academy of Nursing Editors |
| INARS | International Association of Rubenfeld Synergists |
| INBLF | International Network of Boutique Law Firms |
| INCA | Indiana Night Club Association |
| INDA | International Nonwovens Disposables Association |
| INES | International Network of Engineers and Scientists |
| INNS | International Neural Network Society |
| INQAAHE | International Network for Quality Assurance Agencies in Higher Education |
| INRG | International Neuroblastoma Risk Group |
| INRG | Inter-Networking Research Group |