| icn | OpenFlight Model |
| icns | Mac OS X Icon Resource File |
| iconbox | IconBox Data |
| iconset | Mac OS X Icon Resource File |
| icontainer | CandyBar iContainer Data |
| icr | Impromptu Content Report |
| icsalarm | iCal Alarm Data |
| ict | Cadence ASCII Interconnect Technology File |
| icursorfx | iCursor Effect |
| icx | Windows CE Remote Call Profiler Summary View |
| icxs | iTunes Internal Data |
| id | Lotus Notes User ID File |
| id2 | Live Messenger Custom Emoticon Metadata |
| id3 | iData v3 Database |
| id3 | ID3 Metadata |
| id31 | Helium Music Manager id3 Tags Export |
| id32 | Helium Music Manager id3 Tags Export |
| id3tag | MP3 Skype Recorder Temporary Data |
| idat | Illumina BeadArray Data |
| idata | iData v2 Database |
| idb | InfoStat Database |
| idb | Intuit Quicken Home Inventory Data File |
| idb2 | Q-MIDI Instrument Database |
| idb2 | InfoStat Database 2 |
| idcl | Autodesk Inventor Content Library |
| idf | Intermediate Data Exchange File |
| idif | Netscape Navigator Addressbook Identification Data |
| idj | IDATG Java GUI Info File |
| idms | Adobe InDesign Snippet |
| idoc | SAP IDoc File |
| idos | Plaque Simulator Custom Isodose Data |
| idpp | Adobe InDesign Preflight Profile |
| idrc | Adobe InDesign Resource |
| idrm | Tekla ID Mapping File |
| idu | Interleaf Desktop Utility |