FSI
- Bidirectional text
- FRISK Software International
- FSI International
- Federation of Italian Socialists
- Ferrovie dello Stato Italiane
- Financial Secrecy Index
- Financial Stability Institute
- Financial services industry
- Flame spread index
- FlightSafety International
- Floor space index
- Florida Space Institute
- Fluid-structure interaction
- FontShop International
- Foreign Service Institute
- Foreign Service Institute, India
- Forest Survey of India
- Fox Sports International
- Fragile States Index
- Free Sons of Israel
- Freeman Spogli Institute for International Studies
- Frequency scanning interferometry
- Fuel stratified injection
- Full spectral imaging
- Fédération Ivoirienne du Scoutisme
- Henry Post Army Airfield
- IBM Power microprocessors
- Internal Security Forces
- Italian Chess Federation