Organizations
- Samsung Semiconductor Inc., a Korean electronics company
- Scuba Schools International, a diver training organization
- Space Science Institute, an American nonprofit organisation based in Boulder, Colorado
- Space Services Inc., a team of companies investigating new commercial opportunities in space
- Space Studies Institute, an American non-profit organisation based in Mojave, California
- The Spastics Society of India, an organization based in India
- Spatial Sciences Institute, a professional body in the Asia-Pacific region
- Statens Serum Institut, the Danish State Serum Institute
- Strategic Studies Institute, the United States Army War College institute for geostrategic and national security research and analysis
- Sustainable Sciences Institute, a San Francisco-based organisation building local capacity in developing countries
- Statens strålskyddsinstitut (Swedish Radiation Safety Authority), a Stockholm-based regulatory and research government agency
- Survey Sampling International (SSI), a global provider of sampling solutions in marketing research
- Swedish Society for Interlingua, a society that encourages the active use of Interlingua in Sweden
- The General Directorate for State Security Investigations Egypt, 's internal security force
- Sahaviriya Steel Industries, a Thai steel producer
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