| Abbreviation | Definition |
|---|---|
| ISMC | International Society of Motor Control |
| ISMP | Institute for Safe Medical Practices |
| ISMP | Institute for Safe Medication Practices |
| ISMP® | Institute for Safe Medical Practices |
| ISN | Immigrants Support Network |
| ISO | Imamia Students Organization |
| ISO | International Student Organization |
| ISOC | Internation Society Of Cultures |
| ISODE | International Standards Organization Development Environment |
| ISON | In Service Of the Needy |
| ISOP | Infantile Scoliosis Outreach Program |
| ISOP | International Society Of Pharmacovigilance |
| ISPA | Iowa State Police Association |
| ISPCA | Irish Society For The Prevention of Cruelty to Animals |
| ISRA | Illinois State Rifle Association |
| ISRA | Indiana State Reading Association |
| ISRA | International Society for Research on Aggression |
| ISRS | International Stereotactic Radiosurgery Society |
| ISSL | International Society for Social Law |
| ISS-USA | International Social Service - United States of America Branch |