| Abbreviation | Definition |
|---|---|
| IREG | International Rating Expert Group |
| IRF | Incentive Research Foundation |
| IRF | Incentive Research Foundation's |
| IRF | International Renaissance Foundation |
| IRF | International Renaissance Foundation's |
| IRF | International Rhino Foundation |
| IRF | Islamic Reseach Foundation |
| IRF | Islamic Research Foundation |
| IRF | Island Resources Foundation |
| IRPF | International Real Property Foundation |
| IRRF | International Retinal Research Foundation |
| ISDF | Independence School District Foundation |
| ISDF | Indus Sustainable Development Foundation |
| ISDF | International Street Dog Foundation |
| ISF | Ian Somerhalder Foundation |
| ISF | Indochina Starfishfish Foundation |
| ISF | Israel Science Foundation |
| ISFA | Independent Schools Foundation Academy |
| ISFP | Improving Selection to the Foundation Programme |
| ISFS | International School for Foundation Studies |