| Illinois State Science Assessment | Academic & Science |
| Islamic Society of Seacoast Area | Academic & Science |
| Islamic Society of the Seacoast Area | Academic & Science |
| Indian Academy of Social Science | Academic & Science |
| International Ship Suppliers Association | Business |
| International Securities Services Association | Business |
| International Sanitary Supply Association | Business |
| International Sports Sciences Association | Business |
| Inter Scholastic Sailing Association | Business |
| International Slurry Surfacing Association | Business |
| International Studies Schools Association | Business |
| International Sailing School Association | Community |
| Illinois Search Staffing Association | Community |
| International Song Singer Association | Community |
| International Students and Scholars Association | Community |
| Internet Systems Security Association | Community |
| Information Science Student Association | Community |
| Individual Service And Support Advocacy | Community |
| International Social Security Association | Community |
| International Sociology of Sport Association | Community |
| Islamic State in Sunni America | Community |
| Information Systems Schools of Africa | Community |
| International Slalom Skateboarding Association | Community |
| Information System Security Awareness | Computer Technology |
| Information Systems Security Association | Computing |
| Information Security for South Africa | Computing |
| Information System Security Association | Computing |
| Integrated Software Safety Analysis | Computing |
| Iternational Scale Soaring Assc | General |
| Instant Satisfaction Simply Assured | General |
| Industrial Security Staff Approval | General |
| Information Systems Support Activity | General |
| IATA Standard Safety Assessment | General |
| Intelligence Specialist Seaman Apprentice | Governmental |
| International Space Station Alpha | International |
| International Society for the Study of Argumentation | International |
| Inter-service Support Agreement | Military and Defence |
| Interoperable Signed Sender Address | Networking |
| International Sports Science Association | Sports |
