| Islamic Sciences and Research Academy | Academic & Science |
| International Shari’ah Research Academy | Academic & Science |
| International Society for Research Activity | Academic & Science |
| Idaho Society of Radio Amateurs | Academic & Science |
| International Society for Research on Aggression | Academic & Science |
| Institute of State and Regional Affairs (Pennsylvania State University) | Academic & Science |
| Islamic Studies and Research Association | Academic & Science |
| Illinois Summer Research Academy | Academic & Science |
| Intelligent Systems Robotics and Automation | Academic & Science |
| Idaho Society of Radio Amateurs, Inc. | Academic & Science |
| Intermarket Symbols Reservation Authority | Business |
| Indiana Street Rod Association | Community |
| Illinois State Rifle Association | Community |
| Indiana State Reading Association | Community |
| International Slot Racing Association | General |
| Iowa Street Rod Association | General |
| International Star Riders Association | General |
| IL State Rifle Assoc | General |
| Information Security Risk Assessment | General |
| Information Security Risk Analysis | General |
| Institut Senegalais de Recherches Agricoles | General |
| Image Space Reconstruction Algorithm | General |
| Institute of State and Regional Affairs | Governmental |
| Industrial Site Recovery Act | Governmental |
| Industrial Site Recovery Act (New Jersey) | Governmental |
| International Symposium on Robotics and Automation | International |
| Illinois State Racquetball Association | Sports |
| Illinois Squash Racquets Association | Sports |
| International Sim Racing Association | Sports |
