| Staple Inn Actuarial Society | Academic & Science |
| Somerset Industrial Archaeological Society | Academic & Science |
| Science Industry Assessment Service | Academic & Science |
| School of International and Area Studies | Academic & Science |
| Student Information Access System | Academic & Science |
| School of Indigenous Australian Studies | Academic & Science |
| Student Investment Advisory Service | Business |
| Securities Investors Association Singapore | Business |
| Specific Independent Auditing Standard (China) | Business |
| Student Investment Advisory Services | Business |
| Statements on Internal Auditing Standards | Business |
| Statutory Inspection of Anglican Schools | Community |
| School of Interdisciplinary Arts and Sciences | Community |
| Sussex Industrial Archaeology Society | Community |
| Standard Intel Architecture Server | Computing |
| Spina iliaca anterior superior | General |
| Sociedade Ibgeana de Assistência e Seguridade | General |
| Shropshire Independent Advocacy Scheme | General |
| Solihull Integrated Addiction Services | General |
| Spectroscopy in a Suitcase | General |
| Security Intelligence Analysis Service | General |
| Societa Incremento Automobilistico e Sport | General |
| Shanghai International Auto Show | General |
| Sacramento International Auto Show | General |
| Seattle International Auto Show | General |
| SAFI Institute of Advanced Study | Governmental |
| Southasia Institute of Advanced Studies | Governmental |
| Summer Institute for Academic Success | Governmental |
| Salzburg Institute of Actuarial Studies | Governmental |
| Some Institutes for Advanced Study | Governmental |
| Societa Iniziative Autostradali e Servizi | Governmental |
| Slightly Increased Attack Speed | Governmental |
| Scandinavian Institute of African Studies | Regional |
