| Extension | Summary |
|---|
| .I | Visual Studio Intermediate File |
| .I00 | DVD Shrink Part 1 File |
| .I01 | DVD Shrink Part 2 File |
| .I02 | DVD Shrink Part 3 File |
| .I3D | Houdini Image 3D File |
| .I3PACK | Point Blank Game Data File |
| .I5Z | IUCLID 5 Import/Export File |
| .I6 | Inform 6 Source Code File |
| .I6T | Inform 6 Template |
| .I7 | Inform 7 Source Code File |
| .I7X | Inform 7 Extension Source Code File |
| .I7XP | Inform 7 Extension Project |
| .IAA | INTUS Audio Archive |
| .IADACTION | iAd Producer Plugin Action Template |
| .IADCLASS | iAd Producer Plugin Class summary File |
| .IADCOMPONENT | iAd Producer Plugin Component File |
| .IADPAGE | iAd Producer Plugin Page Template |
| .IADPLUG | iAd Producer Plugin |
| .IADPROJ | iAd Producer Project |
| .IADSTYLE | iAd Producer Plugin Style Template |
| .IAF | Outlook Internet Account File |
| .IAM | Inventor Assembly File |
| .IAS | Intermodulation Analysis System File |
| .IB | InterBase Database |
| .IB2 | IncrediBots 2 Saved Challenge File |
| .IB3 | IncrediBots 3 Saved Challenge File |
| .IBA | Lectra Clothing Design Pieces File |
| .IBADR | IsoBuster Address File |
| .IBATEMPLATE | iBooks Author Document Template |
| .IBB | ImgBurn Project File |
| .IBCD | InstantBingoCard Document |
| .IBCH | IncrediBots Challenge File |
| .IBD | MySQL InnoDB Table |
| .IBDAT | IsoBuster Data File |
| .IBG | ImgBurn Graph File |
| .IBK | IncrediMail Account Backup File |
| .IBOOKS | Multi-Touch iBook |
| .IBP | IsoBuster Managed Image Information File |
| .IBPLUGIN | Interface Builder Plug-in |
| .IBQ | IsoBuster Managed Image File |
| .IBRE | IncrediBots Replay File |
| .IBRO | IncrediBots Robot File |
| .IBT | Texture and Model File |
| .IC1 | Low Resolution Imagic Graphics File |
| .IC2 | Medium Resolution Imagic Graphics File |
| .IC3 | High Resolution Imagic Graphics File |
| .IC3D | IC3D Scene File |
| .ICA | Citrix ICA File |
| .ICAL | iCalendar File |
| .ICALENDAR | iCalendar File |
| .ICALEVENT | iCal Event File |
| .ICALTODO | iCal To Do File |
| .ICAP | InCopy Package File |
| .ICBU | Calendar Backup File |
| .ICC | ICC Profile |
| .ICD | Installable Client Driver File |
| .ICE | ICE File Archive |
| .ICF | Zoom Router Configuration File |
| .ICG | Image Comparer Gallery File |
| .ICHAT | iChat Saved Chat Log |
| .ICL | Windows Icon Library File |
| .ICM | Image Color Matching Profile |
| .ICMA | InCopy Assignment File |
| .ICML | InCopy Document |
| .ICMOD | Inner Core Minecraft PE Mod File |
| .ICMT | InCopy Template |
| .ICN | Windows Icon File |
| .ICNS | macOS Icon Resource File |
| .ICO | Icon File |
| .ICON | Icon Image File |
| .ICONPACKAGE | IconPackager Theme File |
| .ICONSET | Mac OS X Icon Set Folder |
| .ICONTAINER | CandyBar iContainer File |
| .ICPR | IconUtils Project File |
| .ICR | Image Comparer Results File |
| .ICS | Calendar File |
| .ICST | InCopy Document Preset File |
| .ICURSORFX | iCursor Effect File |
| .ID | Lotus Notes User ID File |
| .ID2 | Windows Live Messenger Emoticon File |
| .ID3TAG | MP3 Skype Recorder Temporary File |
| .IDAP | Adobe InDesign Assignment Package |
| .IDB | Visual Studio Intermediate Debug File |
| .IDC | Internet Database Connector File |
| .IDCL | Inventor Desktop Content Library File |
| .IDDX | Static Default File |
| .IDE | Inventor iFeature File |
| .IDEA | IntelliJ IDEA Settings Directory |
| .IDEPLUGIN | Xcode IDE Plug-in |
| .IDF | MIDI Instrument Definition File |
| .IDI | EVA Controller Event Log |
| .IDL | Interface Definition Language File |
| .IDLK | Adobe InDesign Lock File |
| .IDML | Adobe InDesign Markup Language File |
| .IDMS | Adobe InDesign Snippet |
| .IDPK | Adobe InDesign Package for GoLive File |
| .IDPP | Adobe InDesign Preflight Profile |
| .IDT | Windows Installer Database Text Archive File |
| .IDV | Inventor Design View File |
| .IDW | Inventor Drawing |
| .IDX | Index File |
| .IDX0 | Runescape Cache Index File |
| .IDX255 | Runescape Cache File |
| .IES | IES Photometric Data File |
| .IF | Procedimientos-Uno IFWin Project File |
| .IFAITH | iFaith SHSH File |
| .IFC | Industry Foundation Classes File |
| .IFCXML | Industry Foundation Classes XML File |
| .IFCZIP | Compessed IFC File |
| .IFD | InForm Document |
| .IFF | Interchange File Format |
| .IFICTION | iFiction Metadata File |
| .IFL | 3ds Max Image File List |
| .IFM | Informed Form Data Document |
| .IFO | DVD-Video Disc Information File |
| .IFP | GTA Animation File |
| .IFS | InfoSlips Package |
| .IFW | INTUS Firmware File |
| .IGB | Intrinsic Graphics Binary File |
| .IGC | Anime List Builder Input File |
| .IGES | IGES Drawing File |
| .IGG | SuiteProfiler Color Map File |
| .IGI | Indigo Image File |
| .IGM | Indigo Renderer Material File |
| .IGMA | INTUS Graph Mask Archive |
| .IGN | RoboHelp Ignore List File |
| .IGP | Igor Published Music Notation File |
| .IGQ | Indigo Queue File |
| .IGR | Quest3D Channel Group Layout File |
| .IGS | IGES Drawing File |
| .IGT | iGrafx Document Template |
| .IGX | iGrafx Document |
| .IGZ | Intrinsic Alchemy Asset |
| .IHW | IN-HEH Timeline Workspace |
| .IHX | IN-HEH Timeline Database |
| .II | IconWorkshop Extended Information File |
| .IIF | Intuit Interchange Format File |
| .IIL | CleanSweep Installation Log |
| .IIM | iMacro Macro File |
| .IIP | ThinAnywhere Configuration File |
| .IIQ | Phase One RAW Image |
| .IIT | Install Creator Project File |
| .IIX | Translation Memory Index File |
| .IK | CryENGINE IK Animation File |
| .IKF | INTUS Keyboard File |
| .IKMP | IK Multimedia Preset FIle |
| .ILBM | Interleaved Bitmap Image |
| .ILDOC | QuickSilver Document |
| .ILG | InstallScript Log File |
| .ILK | Incremental Linking File |
| .ILOGICVB | iLogic VB File |
| .IM4P | IMG4 Payload File |
| .IMA | Disk Image |
| .IMAGE | Apple Disk Image |
| .IMAGEPORTFOLIOLIBRARY | Painter Image Portfolio Library |
| .IMAPMBOX | IMAP Mailbox |
| .IMD | ImageDisk Disk Image File |
| .IME | Windows Input Method Editor File |
| .IMF | Id Music File |
| .IMG | Macintosh Disk Image |
| .IMG3 | iPhone IMG3 File |
| .IMGA | Aleph One Image File |
| .IMI | Magellan Map File |
| .IMJ | JFIF Bitmap Image |
| .IML | ACT! Internet Mail Message |
| .IMM | iMindMap Map File |
| .IMMODULES | GTK+ Module File |
| .IMOVIEEVENT | iMovie Event File |
| .IMOVIELIBRARY | iMovie Library File |
| .IMOVIEMOBILE | iOS iMovie Project File |
| .IMOVIEPROJ | iMovie Project File |
| .IMOVIEPROJECT | iMovie Project |
| .IMP | Improv Spreadsheet |
| .IMPORT | Godot Engine Import Settings File |
| .IMR | Impromptu Report File |
| .IMT | My Time Data File |
| .IMTX | iMindMap Template File |
| .IMX | iMindMap Map File |
| .IMY | iMelody Ringtone File |
| .IMZ | WinImage Compressed Disk Image |
| .IN | Spyware File |
| .INC | Include File |
| .INCA | InCopy CS3 Assignment File |
| .INCD | InCopy Document |
| .INCP | InCopy CS3 Package File |
| .INCT | InCopy Template |
| .INCX | InCopy CS3 Interchange File |
| .IND | Memory Stick Formatting File |
| .INDB | Adobe InDesign Book File |
| .INDD | Adobe InDesign Document |
| .INDESIGNPLUGIN | Adobe InDesign Plug-in |
| .INDK | Adobe Shortcut Set File |
| .INDL | Adobe InDesign Library |
| .INDP | Adobe InDesign CS3 Package File |
| .INDS | Adobe InDesign Snippet File |
| .INDT | Adobe InDesign Template |
| .INETLOC | Internet Location |
| .INF | Inform Source Code File |
| .INFO | Generic Information File |
| .INFOPATHXML | Microsoft InfoPath Form |
| .INFORM | Inform Project |
| .INF_LOC | Windows Driver Information Cache File |
| .ING | MasterCook Ingredients File |
| .INI | Gravis UltraSound Bank Setup File |
| .INJB | InDesign Job Bag File |
| .INK | Pocket PC Handwritten Note |
| .INL | C++ Inline File |
| .INLK | Adobe InDesign Lock File |
| .INLX | Adobe InDesign Interchange Library |
| .INM | FaxMaster Document |
| .INMS | Adobe InDesign Menu Set File |
| .INO | Arduino Sketch |
| .INP | MAME Replay File |
| .INPROGRESS | Time Machine Backup Progress File |
| .INS | Internet Settings File |
| .INSP | Insta360 Panoramic Image |
| .INSTALLLOG | .NET Assembly Installation Log |
| .INSTALLSTATE | .NET Assembly Uninstaller File |
| .INSV | Insta360 Panoramic Video |
| .INT | Intellivision Game ROM File |
| .INTERNETCONNECT | Apple Internet Connect Document |
| .INV | INVedit File |
| .INX | Inkscape Extension Descriptor File |
| .IOBIT | Advanced SystemCare Rollback File |
| .ION | File summary File |
| .IOPLIST | Mac OS X IOPLIST File |
| .IP | IconPackager Theme File |
| .IPA | iOS Application |
| .IPALIAS | iPhoto Alias File |
| .IPCC | iPhone Carrier Bundle |
| .IPCH | Intellisense Precompiled Header File |
| .IPD | BlackBerry Backup File |
| .IPF | Interchangeable Preservation File |
| .IPG | iPod Game File |
| .IPHOTO | iPhoto Library File |
| .IPHOTOPROJECT | iPhoto Print Project |
| .IPICK | iPick Football Image |
| .IPJ | Inventor Project File |
| .IPK | Itsy Package |
| .IPL | GTA Item Placement File |
| .IPLB | iPhoto Library Archive Document |
| .IPMETA | Apple iPhoto Metadata File |
| .IPN | Inventor Presentation File |
| .IPOD | Rockbox Firmware File |
| .IPP | Inline Guard Macro File |
| .IPR | InstallShield Professional Project File |
| .IPROJECT | iClone Project File |
| .IPS | Internal Patching System Patch File |
| .IPSPOT | iPhoto Spot File |
| .IPSW | iPod and iPhone Software Update File |
| .IPT | Inventor Part File |
| .IPTHEME | IconPackager Raw Theme File |
| .IPX | IPIX Image |
| .IPYNB | Jupyter Notebook |
| .IQ4 | IQ4E Controller Strategy File |
| .IQMOL | IQmol Archive |
| .IQY | Internet Query |
| .IRCAM | IRCAM Sound File |
| .IRCP | SpeedGrade IRIDAS Composite File |
| .IRF | CCTV DVR H.264 Video File |
| .IROCK | intelliRock Sensor Data File |
| .IROS | Adobe Save For Web Settings File |
| .IRP | Internet Researcher Project File |
| .IRR | Irrlicht 3D Scene |
| .IRRMESH | Irrlicht Static Mesh File |
| .IRS | Adobe Save For Web Settings |
| .IRX | Brewer Irradiation File |
| .IS1 | Synergy/DE Data Index File |
| .IS2 | Thermal Image Data File |
| .ISALE | iSale Auction |
| .ISALETEMPLATE | iSale Template |
| .ISALLIC | iSale License File |
| .ISC | Xilinx Device Configuration File |
| .ISD | Flexera InstallShield Dialog Box File |
| .ISE | InstallShield Express Project File |
| .ISF | Inspiration Flowchart Document |
| .ISH | ISH Compressed Archive |
| .ISH1 | Animation-ish Wiggledoodle-ish Document |
| .ISH2 | Animation-ish FlipBook-ish Document |
| .ISH3 | Animation-ish Advanced-ish Document |
| .ISM | InstallShield Project File |
| .ISMA | IIS Smooth Streaming Audio File |
| .ISMC | Smooth Streaming Client Manifest File |
| .ISMV | IIS Smooth Streaming Video File |
| .ISN | Installer Source File |
| .ISO | PlayStation 2 ROM File |
| .ISOZ | Compressed Arbortext IsoDraw Illustration |
| .ISP | IIS Internet Service Provider Settings |
| .ISPC | Image Surfer Pro Collection File |
| .ISR | GoMoku Game File |
| .ISS | InstallShield Silent Response File |
| .IST | InstallShield Project Template File |
| .ISU | InstallShield Uninstaller Script |
| .ISX | SimulationX Project |
| .ISZ | Zipped ISO Disk Image |
| .IT | Impulse Tracker Module |
| .ITA | IconTweaker Theme Archive |
| .ITC | iTunes Cover Flow Data File |
| .ITC2 | iTunes Cover Flow Data File 2 |
| .ITDB | iTunes Database File |
| .ITE | iTunes Extras File |
| .ITEMDATA-MS | Windows 8 Start Screen Item Data File |
| .ITF | Image Tuner File |
| .ITHMB | iPod and iPhone Photo Thumbnails File |
| .ITI | InterActual Skin File |
| .ITK | ScummVM Game Data File |
| .ITL | iTunes Library File |
| .ITLP | iTunes LP Album File |
| .ITLS | iTunes Live Stream URL |
| .ITM | iThink Model File |
| .ITMS | iTunes Music Store Link File |
| .ITMSP | iTunes Store Package |
| .ITN | TomTom Navigator Itinerary File |
| .ITPC | iTunes Podcast Link File |
| .ITR | Icy Tower Replay File |
| .ITS | Internet Document Set |
| .ITT | IconTweaker Theme File |
| .ITW | InTouch With Database File |
| .ITX | ITX Form Template |
| .IUP | Fritz Update File |
| .IUS | InfoTMIC Firmware Update File |
| .IV | Open Inventor Scene Graph File |
| .IV2I | Norton Ghost Incremental Virtual Volume Image |
| .IVA | Dementia.4207 Virus File |
| .IVC | InteliSea Vessel Configuration File |
| .IVD | Bitdefender Incremental Virus Definitions File |
| .IVE | OpenSceneGraph Binary File |
| .IVF | Indeo Video Format File |
| .IVR | Image Worlds File |
| .IVS | Internet Streaming Video |
| .IVT | International Volleyball 2006 Data File |
| .IVUE | Live Picture IVUE Image |
| .IW | Chain Engineering Database File |
| .IWA | iWork Archive File |
| .IWB | IWBasic Source Code File |
| .IWD | Call of Duty Game Data File |
| .IWDGT | iWeb Widget File |
| .IWI | Infinity Ward Texture File |
| .IWM | iWriteMusic Data File |
| .IWS | InstallWatch Scan File |
| .IWXDATA | iWorx Data File |
| .IWZ | InstallShield Express 2 Project File |
| .IX | dtSearch Index File |
| .IX2 | WordPerfect Address Book File |
| .IXA | Ulead Disc Image format |
| .IXB | Ulead Disc Image |
| .IZE | IZArc Archive |
| .IZZ | Isadora Media Control Project |
| .IZZY | Isadora Project |