| Abbreviation | Definition |
|---|---|
| SIRI | Safety Information Resources, Inc. |
| SIRS | Social Issues Research Service |
| SIS | Schengen Information System |
| SIS | Security Industry Specialists |
| SIS | Silicon Integrated Systems |
| SIS | Singcare International Services |
| SIS | Single Instance Store |
| SISC | Specialist Industrial Services Company |
| SISCO | Saudi Industrial Services COmpany |
| SISI | Sisters Inspiring Sisters Incorporated |
| SISO | Samsung India Software Operations |
| SISO | Settlement and Integration Services Organization |
| SIT | Sordina IORT Technologies |
| SIT | Spanish Interpreting Services |
| SITA | Société Internationale de Télécommunications Aéronautiques (in French) International Aeronautical Telecommunications Society |
| SITASA | Silos de Tarragona Servei d'Autoritat (in Catalan) |
| SITC | Swiss Insurance Training Centre |
| SITE | Sindh Industrial Trading Estate |
| SITEC | Sicherheitstechnik (not an acronym) |
| SITEL | Systems International TELemarketing |