| Abbreviation | Definition |
|---|---|
| ISIS | Inspection Services Information System |
| ISIS | International Security Information Service |
| ISIT | Interagency Spatial Information Team |
| ISM | Industrial Security Manual |
| ISO | Immunization Safety Office |
| ISP | Information Security Program |
| ISP | Infrastructure Service Provider |
| ISP | International Security Passport |
| ISRC | International Standard Recording Code |
| ISS | Immigrant Social Services |
| ISS | Intelligence Systems Secretariat |
| ISTEA | Intermodal Surface Transportation Efficiency Act |
| ISU | In Situ Update |
| ISW | Institute for Study of War |
| IT | International Terrorism |
| ITA | Improved Trade Agreement |
| ITA | Income Tax Act |
| ITA | International Trade Administration |
| ITAC | Information Technology Advisory Council |
| ITACS | Import Trade Auxiliary Communications System |