SFI
- SFI Foundation
- Safi, Malta
- Santa Fe Institute
- Saturday Football International
- Science Foundation Ireland
- Seattle Film Institute
- Secure Freight Initiative
- SerDes Framer Interface
- Simple Firmware Interface
- Software Freedom International
- Solar cycle
- St. Francis Institution
- Starfleet International
- Students' Federation of India
- Sustainable Forestry Initiative
- Swedish Film Institute
- Swedish for immigrants
- Swimming Federation of India
- Swiss Finance Institute