| Extension | Information |
| X | Alysis SuperDisk Self-extracting Archive |
| X | Amapi 3D Modeling |
| X | Direct3D Object (Microsoft) |
| X | LEX Program File |
| X | Stardent AVS X Image |
| X | Xview Object |
| X | XBLite Program File |
| X01 | Paradox Secondary Index |
| X02 | Paradox Secondary Index |
| X03 | Paradox Secondary Index |
| X04 | Paradox Secondary Index |
| X05 | Paradox Secondary Index |
| X06 | Paradox Secondary Index |
| X07 | Paradox Secondary Index |
| X08 | Paradox Secondary Index |
| X09 | Paradox Secondary Index |
| X1 | X1 Desktop Search Saved Search File (X1 Technologies, Inc.) |
| X10 | X Window Dump Bitmap |
| X11 | X Windows System Window Dump Bitmap |
| X13 | Hooligans |
| X16 | Macromedia Program Extension |
| X32 | Macromedia Program Extension (Macromedia) |
| X3D | x3D and xdart Formats |
| X3D | Xara 3D Project File (Xara) |
| X3F | Sigma Camera RAW Picture File (Sigma) |
| X4M | TeamLinks Mail File Data |
| X5 | Rockwell Software Logix 5 File |
| X64 | C64 Emulator Disk Image |
| XA | Extended Architecture File |
| XA | Playstation Video (Sony Corporation of America) |
| XA | Gear CD Suite File |
| XA | The Sims Extensive Audio (Electronic Arts (Maxis)) |
| XA2 | Exam Editor Question Groups (Nice Productions) |
| XAB | Mail Address Book (Microsoft) |
| XAB | Xenis Mail Address Book |
| XACT | XactScript File (XactCommerce) |
| XAD | eXotic AdLib Format |
| XAN | XANIA Browser |
| XAN | xyALGEBRA File |
| XAP | Xbox Dashboard Script (Microsoft) |
| XAR | Corel Xara Drawing |
| XAR | Xara X Vector Drawing (Xara) |
| XAR | Excel AutoRecover File (Microsoft) |
| XARC | The Longest Journey Sound File (Funcom) |
| XAS | Playstation Video (Sony Corporation of America) |
| XBE | Xbox Executable (Microsoft Corporation) |
| XBF | Database File |
| XBF | Emperor Battle for Dune |
| XBK | SMART Board Slide Collection (SMART Technologies Inc.) |
| XBL | Extensible Binding Language |
| XBL | XBLite Program File |
| XBM | X Bitmap Graphic |
| XBP | XBWML X-Bite.co.uk Markup Language (X-Bite.co.uk) |
| XBS | ETAK MapBase |
| XBW | Crossword |
| XBX | XBox Image File (Microsoft) |
| XB~ | IC File |
| XC | X Server Constant Screen Image Bitmap |
| XC2 | HPXView DACCS Configuration (Haliplex Communication Systems) |
| XCDATAMODEL | Xcode Core Data-based Data Model (Apple Computer, Inc.) |
| XCF | GIMP Image File (The GIMP Team) |
| XCK | Extended Crack File |
| XCL | Xtree for Win Script |
| XCM | CmapTools Exported Concept Map (IHMC) |
| XCN | HPXView DACCS Configuration (Haliplex Communication Systems) |
| XCR | Warlords Battlecry |
| XCS | BuzzLetter Encrypted Stationery Template (StationeryCentral.com, Inc.) |
| XCZ | BuzzLetter Zipped Collection of Encrypted Stationery Templates (StationeryCentral.com, Inc.) |
| XD | CCS-lib.2 Examples Motif-CC File |
| XDB | Norton AntiVirus Update File (Symantec) |
| XDB | HyperCD HyperLOCK (John Galt Media, Inc.) |
| XDE | Tgif-3.0 File |
| XDF | Extended Disk Format Image |
| XDF | Milnta APL Transfer Function |
| XDF | ProWORX Nxt Extended Memory Data (Schneider Electric) |
| XDF | Workshare Synergy File |
| XDF | X68000 Image File |
| XDIM | Multi-Channel Server (MCS) Markup Editor XDIME Document (Volantis Systems Ltd.) |
| XDK | XML Development Kit Project (Republicorp Virtual Media) |
| XDO | OutDo Outline File (Aspevia Systems) |
| XDP | UNIX File |
| XDR | BizTalk XML-Data Reduced Schema (Microsoft) |
| XDRUID | XDIME Player Skin (Volantis Systems Ltd.) |
| XDR_TOR | Insight II Binary Torsion File (Accelrys Software Inc.) |
| XDS | OpenGL Performer Script |
| XDS | XDS X-ray Detector Software |
| XDS | Symantec Store Download Manager Partial Download (Symantec Corporation) |
| XDSL | D-Link Router UK Firmware Update File (D-Link Systems, Inc.) |
| XDT | Xscript Data Packet (Codec Games) |
| XDW | DocuWorks File (Fuji Xerox Co., Ltd.) |
| XDW | Milnta APL Transfer Function |
| XEC | Afaria (XcelleNet) |
| XEF | eManager Form Data (X-Genics Ltd.) |
| XEM | eManager Metering Unit Credits for File Use (XGenics Ltd.) |
| XEP | eManager File Packing Definition (XGenics Ltd.) |
| XES | eManager XML UI Definition for Skins (XGenics Ltd.) |
| XET | eManager XML Definition of eManager Process (XGenics Ltd.) |
| XEV | eManager XML Autoupdate Definition (X-Genics Ltd) |
| XEX | KERMIT Control File |
| XEX | Renamed .EXE File |
| XEX | Xbox Executable (Microsoft Corporation) |
| XEZ | eManager Template Package (X-Genics Ltd.) |
| XFC | Docuprint N17 Printer Firmware (Xerox) |
| XFD | XML Form in XFDL Format |
| XFD | Atari Disk Image (Atari) |
| XFD | Acu4GL Extended File Description (Acucorp, Inc.) |
| XFDF | Acrobat Forms Document (Adobe) |
| XFDL | XML Form in XFDL Format |
| XFI | LaTex Figures File |
| XFM | Audition Transform Effect (Adobe) |
| XFM | OmniForm XML Format |
| XFN | Ventura Printer Font |
| XFR | Symantec Norton Anti-Virus Corporate Version Failed Update |
| XFR | Ventura Publisher Bitmap Editor Font File |
| XFR | Xfrog Vegetation File (greenworks organic-software) |
| XFS | eRacer Sound File |
| XFS | GunBound (Softnyx) |
| XFT | ChiWriter 24 Pin Printer Font |
| XFT | LiveCycle Designer Form (Adobe) |
| XFX | Fax File |
| XG0 | Database Index; Paradox Secondary Index |
| XG1 | Database Index; Also XG2, XG3... |
| XG1 | Techno Toys XG-909 MIDI Drum Machine File |
| XG2 | Database Index; Also XG3, XG4… |
| XG3 | Database Index; Also XG4, XG5… |
| XG4 | Database Index; Also XG5, XG6… |
| XG5 | Database Index; Also XG6, XG7… |
| XG9 | Techno Toys XG-909 MIDI Drum Machine File |
| XGL | MegaBitz Graphics Language File |
| XGM | Techno Toys XG-909 MIDI Drum Machine File |
| XGO | GeoConcept Add-On (GeoConcept SA) |
| XGO | LogMate for Windows File |
| XGO | Paradox Database-related File |
| XGP | PicturePlayer Password Protected Files (PicturePlayer) |
| XGR | Graph Edit XML Graph (Microsoft) |
| XGS | PicturePlayer Scrambled Files (PicturePlayer) |
| XGZ | MegaBitz Vector Drawing |
| XHD | HappyFish XML Data File (ThirstyCrow) |
| XHDML | XML Version of HDML File |
| XHESSIAN | Insight II Hessian File (Accelrys Software Inc.) |
| XHT | Extensible HyperText Markup Language File |
| XHTM | Extensible HyperText Markup Language File |
| XHTML | Extensible HyperText Markup Language File |
| XHTML | Libxml HTML File |
| XI | Fast Tracker 2 Instrument |
| XI | ScreamTracker Instrument File |
| XIF | eXtended Image File Format |
| XIF | Often a Fax Image (TIFF) File |
| XIF | [Removed by request] [Removed by request] (ScanSoft, Inc.) |
| XIF | Wang Image File |
| XIF | Xerox Image File |
| XIF | [Removed by request] [Removed by request] (ScanSoft, Inc.) |
| XIM | X11 Xim Toolkit Bitmap |
| XIN | OmniMark Include File (Stilo) |
| XIP | Hotbar Image Compression Format |
| XIP | HP95 Execute-in-place Program |
| XIP | Xbox Dashboard (Microsoft) |
| XIX | IIS NNTP Subject Lists (Microsoft) |
| XJS | WinExplorer Java Script |
| XJT | Compressed GIMP Image with Properties of GIMP |
| XJTGZ | Compressed GIMP Image with Properties of GIMP |
| XJTZ2 | Compressed GIMP Image with Properties of GIMP |
| XKS | IBM Softcopy Reader PDF Extended Bookshelf File (IBM) |
| XL | Excel Spreadsheet (Microsoft) |
| XL | Old Amiga Movie Format |
| XL | XBLite Program File |
| XL$ | Modem Bitware Fax Disk2 File |
| XLA | Excel Add-in (Microsoft) |
| XLA | Xlib Archive |
| XLA | Data Import aka Dimport Translation Table (DATAIR Employee Benefit Systems, Inc.) |
| XLB | Excel Worksheet (Microsoft) |
| XLC | Excel Chart (Microsoft) |
| XLD | Excel Dialog (Microsoft) |
| XLE | Cooktop File |
| XLF | XLIFF Document |
| XLG | AutoCAD XREF Log (Autodesk, Inc.) |
| XLG | Xnetech Engraving Logo File |
| XLK | Excel Backup (Microsoft) |
| XLL | Excel Add-in (Microsoft) |
| XLM | Excel Macro (Microsoft) |
| XLO | Inventor Export Journal (Autodesk, Inc.) |
| XLR | Works Spreadsheet or Chart (Microsoft Corporation) |
| XLS | Excel Worksheet (Microsoft) |
| XLS | Works Spreadsheet (Microsoft) |
| XLSENX | egis Encrypted Excel XLS File (HiTRUST Inc.) |
| XLSHTML | Excel HTML Document (Microsoft) |
| XLSMHTML | Excel Archived HTML Document (Microsoft) |
| XLSX | Excel Microsoft Office Open XML Format Spreadsheet (Microsoft Corporation) |
| XLSXENX | egis Encrypted Excel Open XML XLSX File (HiTRUST Inc.) |
| XLT | Excel Template (Microsoft) |
| XLT | Lotus Translation Table (IBM) |
| XLT | Procomm Plus Translation Table |
| XLTHTML | Excel HTML Template (Microsoft) |
| XLV | Excel VBA (Microsoft) |
| XLW | Excel Workspace (Microsoft) |
| XLX | XoloX Incomplete Download File |
| XLXML | Excel XML Worksheet (Microsoft) |
| XM | Fast Tracker 2 Extended Module |
| XM | Sound File |
| XMAP | File That Controls How XML/XSL Gets Served |
| XMB | X-Wing Mission Briefing File |
| XMD | GameJack Virtual CD or DVD Image (S.A.D. GmbH.) |
| XMD | OmniMark Source Code (Stilo) |
| XMF | Milnta APL Transfer Function |
| XMF | Extensible Music File Format (MIDI Manufacturers Association Incorporated) |
| XMF | eXtensible Data Model and Format (XDMF) |
| XMFG | MediaForge Runtime Player Distribution Project (XMLAuthor, Inc.) |
| XMH | XMap Handheld Street Atlas USA Map and Route File (Delorme) |
| XMI | EverQuest File |
| XMI | Winamp Extended MIDI File |
| XMI | XML Metadata Interchange Format |
| XMI | XMill Compressed XML (Dan Suciu, AT&T Labs-Research and Hartmut Liefke, University of Pennsylvania) |
| XML | Extensible Markup Language File |
| XMLBACKUP | EnABLE Backup File (Energy Scitech Ltd.) |
| XMP | Graphic File |
| XMP | Spice Pspice Library File |
| XMP | Adobe Extensible Metadata Platform (Adobe) |
| XMP | XMap Project Data (Delorme) |
| XMS | AutoCAD External Message (Autodesk, Inc.) |
| XMS | ViewCafT XML Markup Session |
| XMS | XMS-Tracker |
| XMT_TXT | Parasolid CAD File |
| XMV | Milnta APL Transfer Function |
| XMX | AutoCAD External Message Compiled File (Autodesk, Inc.) |
| XMX | Character Set File |
| XMZ | Fasttracker 2/Extended Module |
| XMZ | MegaView XGL Movie |
| XNF | Standard Network File Form |
| XNG | OM2 911 Xchange Version 6 Document |
| XNG | FishXing Culvert Data File (Stream Systems Technology Center, USDA Forest Service) |
| XNK | Exchange Shortcut (Microsoft) |
| XNML | NML Language Language Extension (NevoSoft) |
| XNT | Spice Pspice Library File |
| XOF | RenderMorphics |
| XOI | eZediaMX and eZedia Player Locked Presentation Document |
| XOM | OmniMark Source Code (Stilo) |
| XOS | Xaos Tools Bitmap Image |
| XOT | Xnetech Job Output File |
| XP | System Utility File |
| XPA | SoniqSync Extended Playlist (SoniqCast, LLC) |
| XPB | XPB! Basic Source Code (Tony D. Jones) |
| XPC | ActionReplay Saved Code (Datel Design and Development Ltd.) |
| XPF | X-Protector Project (The Xprotector Team) |
| XPF | XaoS Position File (Jan Hubicka, Thomas Marsh, Zoltan Kovacs and Others) |
| XPI | Mozilla/Firefox Browser Extension Archive (Mozilla) |
| XPIX | Nonogram Puzzle |
| XPJ | X-Pert for Windows File (Decisive Tools (USA) Pty Ltd) |
| XPK | Spice Pspice Library File |
| XPK | XPK Player Compressed Audio (Data Becker) |
| XPK | Xscript Package (Codec Games) |
| XPL | Music File |
| XPL | WinExplorer Simple Script |
| XPL | Xset Plug-ins File |
| XPL | X-Plane Plug-In (The House of X-Plane) |
| XPM | BMC Software Patrol UNIX Icon File |
| XPM | X Pixmap Graphic |
| XPM | DESQview Macro (Symantec) |
| XPO | Expo Product Tours Project (InstallShield Software Corporation) |
| XPO | Omega Research ProSuite |
| XPO | X-port Version 1 |
| XPP | xCOMPOSER.pro Multimedia Data File |
| XPR | exPresset CD Label (Pressit) |
| XPR | Expression 3 Graphic File (Creature House Ltd.) |
| XPR | XBMCTex/Xbox Media Center Graphic File (XboxMediaCenter Project) |
| XPS | X-port Version 2 |
| XPT | XPCOM Type Library |
| XPT | Dungeons & Dragons Core Rules 2 (Wizards of the Coast, Inc.) |
| XPTHEME | Winstyles Theme (Stardock Corporation, Inc.) |
| XPTOC | XDIME Player Table of Contents (Volantis Systems Ltd.) |
| XPW | Leading Market Technologies EXPO |
| XPW | Accessible FormNet Fillable Form (Intercon Associates Inc.) |
| XPX | XML Format File |
| XPX | RAFTS-XP Macro File (XP Software Inc.) |
| XPX | Dungeons & Dragons Core Rules 2 with Expansion (Wizards of the Coast, Inc.) |
| XPY | MarketBrowser |
| XPY | xpy Settings File (Jan T. Sott) |
| XQT | SuperCalc Macro Sheet |
| XQT | Waffle Executable File |
| XR | Chaos Desktop External Reference File (Chaos systems AB) |
| XR1 | Epic MegaGames Xargon File |
| XRC | wxWindows/wxPython Resource File |
| XREF | AIX Cross Reference File |
| XRF | Cross Reference |
| XRF | Crossreference File |
| XRG | Xscript Game Registry (Codec Games) |
| XRL | XML Résumé Library Résumé |
| XRL | PowerDesigner Report (Sybase, Inc.) |
| XRL | OSCAR Rules File |
| XRP | Experior Practice Management Report (Experior Corporation) |
| XRS | Realplayer Plug-in External Resources File (Real) |
| XRT | Revolution EDX Spectrum Export File in Xraytor Format (4pi Analysis, Inc.) |
| XRW | Architag XRay XML Editor |
| XS | Hummingbird Exceed File |
| XS3 | XESS Worksheet (Applied Information Systems, Inc.) |
| XS4 | XESS Worksheet (Applied Information Systems, Inc.) |
| XS5 | XESS Worksheet (Applied Information Systems, Inc.) |
| XS8 | SIMUL8 |
| XSA | XSA Raw Disk Image (XelaSoft) |
| XSB | Sokoban++ Level File |
| XSC | XML Schema |
| XSC | Xscript Script (Codec Games) |
| XSC | XVI32 Script File (Christian Maas) |
| XSD | XML Schema |
| XSF | Milnta APL Transfer Function |
| XSI | Softimage XSI 3D Model (Avid Technology, Inc.) |
| XSL | FileMaker Database Design Report Template |
| XSL | Steuer2001 File |
| XSL | XML Stylesheet |
| XSLT | XSL Transform File |
| XSM | LEXIS-NEXIS Tracker |
| XSN | xyALGEBRA File |
| XSO | Expresso Project File (Ultrapico) |
| XSQL | Oracle XSQL Servlet XSQL Template File (Oracle Corporation) |
| XSS | Ability Office Spreadsheet (Ability Software) |
| XST | Easy Cross Cross Stitch Design (DOS Version) (Fulford Software Solutions) |
| XST | X-Tract XML Script (DecisionSoft Limited) |
| XSTEP | XStep DWI Maker File |
| XSU | Fortran Libf77 File |
| XSUM | Clapack File |
| XSW | Milnta APL Transfer Function |
| XT | FastTracker Music Track |
| XT* | Crosstalk Related File |
| XTB | LocoScript External Translation Table (LocoScript Software) |
| XTD | XML Type Definition |
| XTG | QuarkXPress Tags File (Quark, Inc.) |
| XTM | CmapTools Exported Topic Map (IHMC) |
| XTML | XML4web Virtual HTML File (Altair Communications Corporation) |
| XTP | XTree Data File |
| XTP | XTreeGold Overlay |
| XTR | RealArcade Compressed Data File |
| XTS | Babya Desktop Shell System Software Extension |
| XTS | CSPro File |
| XUF | Milnta APL Transfer Function |
| XUL | XML User Interface Language (Mozilla) |
| XUW | Milnta APL Transfer Function |
| XV | Khoros Visualization Image File |
| XVB | WinExplorer VB Script |
| XVG | GROMACS Output File |
| XVID | XviD CODEC |
| XVM | VMware Virtual Machine Console (VMware, Inc.) |
| XVP | Xview Package File |
| XVS | Xview Scene Package File |
| XVU | BOClean Database File |
| XWC | Crosstalk for Windows Compiled Script |
| XWD | Crossdown Puzzle File |
| XWD | X Windows Dump |
| XWF | Yamaha XG Works File |
| XWF | Yamaha XG Works File |
| XWI | X-Wing Mission File |
| XWK | Crosstalk Keyboard Mapping |
| XWP | Crosstalk for Windows Phone book |
| XWP | Crosstalk Session |
| XWP | Xerox Writer Text File |
| XWP | XMLwriter XML Editor Project File (Wattle Software) |
| XWS | Crosstalk for Windows Script |
| XWS | Xara Webstyle File (Xara) |
| XWZ | Xset Wizards File |
| XWZ_1 | Xteq X-Setup File |
| XX | Arcedit Temporary File |
| XX | Xxencoded File |
| XXA | Brixx Planner Account Detail Chart (Brixx Solutions Ltd.) |
| XXD | Brixx Planner Calendar File (Brixx Solutions Ltd.) |
| XXE | Xxencoded File |
| XXG | Brixx Planner Graph (Brixx Solutions Ltd.) |
| XXI | GameSpy Arcade |
| XXL | Archive |
| XXP | Brixx Planner Plan File (Brixx Solutions Ltd.) |
| XXR | Brixx Planner Report File (Brixx Solutions Ltd.) |
| XXT | Extension DLL |
| XXX | Compucon/Singer PSW Embroidery Design File |
| XXX | Controlware VJ400 Digital CCTV Recording |
| XXX | Paint Shop Photo Album Panorama (Corel Corporation) |
| XXY | SPARC Executable Script File |
| XY | XYWrite Text File |
| XY3 | XYWrite Text File |
| XY4 | XYWrite IV Document |
| XY4V | XYWrite IV document |
| XYP | XYWrite III Plus Document |
| XYW | XYWrite Windows 4.0 Document |
| XYZ | RPG Maker Graphic Format (Enterbrain, Inc.) |
| XYZ | XMol XYZ |
| XYZ | Förderdiagnose Data File (Bettinger Software) |
| XYZ | Graph Coordinates |
| XYZ | XYZZLY Plug-In for RealPlayer |
| X_B | Parasolid CAD File |
| X_T | Parasolid CAD File |