| Study of Instructional Improvement | Academic & Science |
| Science Integration Institute | Academic & Science |
| Statistics and Its Interface | Academic & Science |
| Science Information Infrastructure | Academic & Science |
| Sidi Ifni | Airport Code |
| Seiko Instruments, Inc. | Business |
| System Integrators, Inc. | Business |
| Strengths, Improvements, And Insights | Business |
| Sprott Incorporated | Business |
| Securities and Investment Institute | Business |
| Investments Inc | Business |
| Smith International, Inc. | Business |
| Steico Industries, Inc. | Business |
| Strategic Investor Initiative | Business |
| Summary of Investment Information | Business |
| Shipper Interest Insurance | Business |
| Social Investment Initiative | Community |
| Sensory Integration International | Community |
| Stellar International Institute | Community |
| Schools Improvement Initiative | Community |
| Scalable Information Infrastructure | Computing |
| Service Independent Intercept | Computing |
| Silicon Image Inc. | Computing |
| Servicio de Impuestos Internos | General |
| Sistema Integral de Información | General |
| Successor In Interest | General |
| Speech Intelligibility Index | General |
| Strong Interest Inventory | General |
| Sustainable Innovation Initiatives | General |
| Seriously Impaired Imagination | General |
| Special Instruction Indicator | General |
| Service Interval Indicator | General |
| Series Two | General |
| Self Inflicted Injuries | Governmental |
| Special Interest Items | Governmental |
| Securities Industry Institute | Governmental |
| Security Industry Institute | Governmental |
| Standards Institution of Israel | Governmental |
| Simulated Iterator And Inquisitor | Governmental |
| The Southern Industrial Institute | Governmental |
| Security Institute of Ireland | Governmental |
| SITIMANI | Indian Railway Station |
| Serum Institute of India | Medical |
| Summary Injury Incidence | Military and Defence |
| Seriously Ill Or Injured | Military and Defence |
| Statement of Intelligence Interest | Military and Defence |
| Spinal Injuries Ireland | Regional |
