SSI
- Rosa Lavín
- SSi Canada
- Safe Superintelligence Inc.
- Sahaviriya Steel Industries
- Samsung Semiconductor Inc.
- Sano Sansar Initiative
- Scottish statutory instrument
- Scuba Schools International
- Selective Service Initiative
- Self-sovereign identity
- Senior station inspector
- Sensitive security information
- Serializable snapshot isolation
- Server Side Includes
- Shared Source Initiative
- Shoulder sleeve insignia
- Silicon Systems Inc.
- Simple Sensor Interface protocol
- Single sign-in
- Single system image
- Sliding scale insulin
- Small-scale integration
- Software Sustainability Institute
- Soil-structure interaction
- Soldier Support Institute
- Solid State Intelligence
- Solid State Interlocking
- Solid State Ionics
- Solid state ionics
- Sonangol Sinopec International
- South Georgia and the South Sandwich Islands
- South Sandwich Islands
- Space Science Institute
- Space Services Inc.
- Space Studies Institute
- Spastics Society of India
- Spatial Sciences Institute
- St. Simons Island
- Staff Sergeant Instructor
- Standing settlement instructions
- Star of the Solomon Islands
- State Security Investigations Service
- Statens Serum Institut
- SteadyShot Inside
- Strategic Simulations Inc
- Strategic Studies Institute
- Strategic sustainable investing
- Stress–strain index
- Students Supporting Israel
- Subsecretaria de Inteligência
- Supplemental Security Income
- Surgical site infection
- Survey Sampling International
- Sustainable Society Index
- Swedish Radiation Safety Authority
- Swedish Society for Interlingua
- Synchronous Serial Interface