| International Student Introduction | Academic & Science |
| International Students Incorporated | Academic & Science |
| Independent Science Investigation | Academic & Science |
| International Student Interexchange | Academic & Science |
| Isisford | Airport Code |
| I Sell International | Business |
| Information Services International | Business |
| Illinois Swimming, Incorporated | Business |
| Indians Service India | Business |
| Innovative Systems, Inc. | Business |
| Installer Supply International | Business |
| Internet Securities Inc | Business |
| Infortext Systems, Incorporated | Business |
| International Sports Images | Business |
| Image Space Inc | Business |
| International Students Inc | Business |
| Instructional Systems Inc | Business |
| Interact Solutions, Inc. | Business |
| Interior Specialists Inc | Business |
| ImageSat International | Business |
| Interactive Solutions Inc | Business |
| Ingredients Solutions Inc | Business |
| Integrated Systems Inc | Business |
| Installation Specialists Inc | Business |
| Integrated Services Inc | Business |
| Integrity, Smartness, and Intellect | Business |
| Institutional Survivability Indicator | Business |
| Initial State Interaction | Chemistry |
| In-situ Interferometer | Chemistry |
| International School of Indiana | Community |
| In-Service Incentive | Community |
| Information Society Index | Community |
| Institute for Scientific Information | Community |
| Inter Symbol Interference | Computer and Networking |
| Increment and Skip On Infinity | Computer Assembly Language |
| In Service Inspection | Computing |
| Integral Systems Incorporated | Computing |
| Image Station Imager | Computing |
| Intelligent Stick Interface | Computing |
| Information Sciences Institute | Computing |
| Intensive Supplemental Instruction | General |
| Iron Sharpening Iron | General |
| Institut Seni Indonesia | General |
| Indeterminate Short Intemode | General |
| International Super Intelligence | General |
| Inayan Systems International | General |
| Import Substitution Industrialisation | General |
| Initial State Interactionand | General |
| Iron Sharpens Iron | General |
| Image Space Incorporated | General |
| International Symposium of Information | General |
| Integrated Strategic Innovation | General |
| Inlet Spray Intercooling | General |
| Indicator of Sexual Interest | General |
| Intelligence and Security Informatics | General |
| Infrared Spatial Interferometer | General |
| India Shall Inspire | General |
| Internally Specified Index | General |
| Industrial Security Integrators | General |
| Independent Study in Idaho | General |
| Inter Spike Interval | General |
| Indomobil Suzuki International | General |
| Intelligent Speed Information | General |
| Intelligent System Identification | General |
| Initiation aux Sciences de l'Ingenieur | General |
| Immigrants Standard Integrationb | Governmental |
| Immigrants Standard Integration | Governmental |
| Indian Standards Institution | Governmental |
| Indian Standard Institute | Governmental |
| Intercollegiate Studies Institute | Governmental |
| Institute For Sustainable Infrastructure | Governmental |
| International Statistical Institute | Governmental |
| Information Security Institute | Governmental |
| Institute of Scientific Information | Governmental |
| Institute for Social Innovation | Governmental |
| Invisible Soldiers of Islam | Governmental |
| Import Substitution Industrialization | Governmental |
| Indian Standards Institute | Indian Organization |
| International Scientific Indexing | International |
| International Succulent Introductions | International |
| International Systems Integration | International |
| Internet Security Infrastructure | Internet |
| in Slang Internet | Internet |
| Incontinence Severity Index | Medical |
| International Sensitivity Index | Medical |
| Insomnia Severity Index | Medical |
| Inter-Stimulus Interval | Medical |
| Insulin Sensitivity Index | Medical |
| Inter-service Intelligence | Military and Defence |
| Inter Systems Intelligence (pakistan) | Military and Defence |
| Insomnia Screening Index | Military and Defence |
| Indian Statistical Institute | Ministry of Statistics and Programme Implementation |
| Ibm Smartcard Identification | Networking |
| Inter-Services Intelligence | Pakistan Government |
| Isisford Airport, Isisford, Queensland, Australia | Regional |
| Initial System Installation | Space Science |
| Instrumentation Support Instruction | Space Science |
| Instrument/spacecraft Interface | Space Science |
| Ice Sports Industry | Sports |
| Illinois Swimming, Inc. | Sports |
| Ice Skating Institute | Sports |
