| idos | Plaque Simulator Custom Isodose Data |
| idpp | Adobe InDesign Preflight Profile |
| idrc | Adobe InDesign Resource |
| idrm | Tekla ID Mapping File |
| idu | Interleaf Desktop Utility |
| idx | Treepad Database Index |
| idx | SmartWare Index Data |
| idx | Microsoft SQL Server Constraints |
| idx | Canon ZoomBrowser EX Database Index |
| idx | Intuit Quicken Index Data |
| idx | Citrix Program Neighborhood Database Index |
| idx | dBASE Database Index |
| idx | LaTeX Unsorted Index Data |
| idz | Autodesk Inventor Compressed Content Library |
| idz | I-DEAS Data |
| ie | MyEclipse Image |
| ied | ISIS Event Data File |
| ief | ISIS Control File |
| ief | iCE CFR Raw Data |
| iei | Image Eye Index Cache |
| ies | IESNA Photometric Data |
| ie_ | Compressed IEC File |
| ifaith | iFaith SHSH Data |
| ifc | Industry Foundation Classes Data |
| ifczip | Compressed IFC Data |
| iff | SmartWare Temporary Merge Data |
| ifi | inFlow Inventory Database Backup |
| ifiction | Zoom iFiction File |
| iflv | InfoLevin Database |
| ifn | IGOR Pro Formatted Notebook File |
| ifs | FractInt IFS File |
| ifs | InfoSlips Package |
| ift | IGOR Pro Formatted Notebook Template File |
| ifw | INTUS Terminal Firmware |
| ig | iSpy Event Data |