| iscf | Intel Schematic Connectivity Format Data |
| isdb | iThink Database |
| ise | InstallShield Express File |
| isg | HSC Chemistry Solgasmix Solver Data |
| isi | Web of Science Databases Output |
| isk | Druvaa inSync Client Key |
| isl | Inno Setup List |
| ism | ISAM Database |
| isml | IIS Smooth Streaming Publishing Point Definition |
| ispc | Image Surfer Pro Collection |
| isr | InstallShield Uninstall Information |
| istg | Imagine Staging File |
| isv | IDL iTools Saved State |
| isw | Intuit Statement Writer Data |
| isw | ZoneAlarm ForceField Data |
| iswp | iTunes iOS Software Update Data |
| is_ | Compressed ISP File |
| it3 | Internet Timer 3 Log |
| itb | iTunes Database |
| itd | IRIT 3D Data |
| itd | SDL Intermediate Translation Document |
| itdb | iTunes Database |
| ite | iTunes Extras |
| itemdata-ms | Windows 8 Start Screen Item Data |
| ith | InTether Receiver Package |
| itk | Insight Segmentation and Registration Toolkit Data |
| itl | iTunes Library File |
| itlp | iTunes LP Album Data |
| itm | iThink Model |
| itm | DMDX Item Data |
| itmx | iThink Model Data |
| itn | TomTom Route Data |
| itp | e-Record Data File |
| itp | GROMACS Include Topology |
| itpc | iTunes Podcast Link |