ISF
- Gaza Strip
- Idaho Shakespeare Festival
- Importer Security Filing
- Incremental sheet forming
- Independent Schools Foundation Academy
- Indian Secular Front
- Information Security Forum
- Ingenieurs Sans Frontieres
- Ink Serialized Format
- Internal Security Forces
- International School Sport Federation
- International School of Florence
- International Seafarers' Federation
- International Skyrunning Federation
- International Snowboard Federation
- International Socca Federation
- International Softball Federation
- International Stabilization Force
- International Sumo Federation
- Internationale Schule Frankfurt Rhein-Main
- Interstitial fluid
- Iraqi security forces
- Israel Science Foundation
- Italian Strategic Fund
- Lexus IS F
- Pakistan Tehreek-e-Insaf
- People's Liberation Army Information Support Force
- Solidarity tax on wealth
- The Idries Shah Foundation
- Video calibration software