| Abbreviation | Definition |
|---|---|
| IRRA | Independent Running Retailers Association |
| IRSA | Indonesian Regional Science Association |
| IRTA | Indiana Retired Teachers Association |
| IRTA | International Racing Teams Association |
| IRVA | Irish Road Victims Association |
| IRVA | Irish Road Victims' Association |
| IRWA | Idaho Rural Water Association |
| IRWA | Illinois Rural Water Association |
| IRWA | Indiana Rural Water Association |
| IRWA | International Right of Way Association |
| IRWA | Iowa Rural Water Association |
| IRWA | Ipswich River Watershed Association |
| ISA | Industrial Supply Association |
| ISA | International Sign Association |
| ISA | International Slackline Association |
| ISA | International Slacklining Association |
| ISA | International Studies Association |
| ISA | International Surfing Association |
| ISAA | Icelandic Sheepdog Association of America |
| ISAA | Illinois State Ambulance Association |