| Extension | Information |
| Q | Win95 Fax Queue |
| Q | Quantum Compressed Archive (Cinematronics) |
| Q0 | Q0 Graphic |
| Q00 | Quicken 2000 File |
| Q01 | Quicken 2001 File |
| Q03 | QuickTax Year 2003 Return (Intuit Canada) |
| Q04 | QuickTax Year 2004 Return (Intuit Canada) |
| Q1 | Winamp Equalizer Settings |
| Q1A | QuickClean Restore Point (Network Associates Technology, Inc.) |
| Q1Q | LunarCell Plug-in File |
| Q1Q | LunarCell Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q2Q | Flexify Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q3D | Quickdraw 3D File |
| Q3D | Quest3D Interactive 3D File (Act-3D B.V.) |
| Q3O | Quick3D Model |
| Q3X | QuickTime QuickDraw 3D Extension (Apple Computer, Inc.) |
| Q4Q | Solar Cell Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q5Q | SuperBladePro Preset |
| Q5R | Melancholytron Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q7Q | India Ink Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q8R | Flood Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q98 | Quicken 98 File |
| Q99 | Quicken 99 File |
| Q9Q | BladePro Graphic Plug-in File |
| Q9R | Glitterato Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| Q9S | Mr. Contrast Photoshop/Paint Shop Pro Plug-In (Flaming Pear Software) |
| QAA | WinQSB Data Input File (John Wiley & Sons, Inc.) |
| QAB | QABUTIL File |
| QAB | SYBYL Binary Field Files |
| QAD | WordPerfect PerfectFit QuickArt NameSpace .WPG Thumbnail (Corel Corporation) |
| QAD | PF QuickArt Document |
| QAG | Norton Desktop Quick Access Group |
| QAP | Omnis Quartz Application File |
| QAX | ExpressTracker Data File |
| QB | Tony Hawk's Pro Skater Script (Neversoft Entertainment) |
| QB1 | Quicken File |
| QBA | QuickBooks Accountant's Copy File (Intuit, Inc.) |
| QBB | QuickBooks Backup File (Intuit, Inc.) |
| QBD | Keyboard Layout |
| QBD | Win3 Quicken File |
| QBE | dBASE IV Saved Query |
| QBE | Example Query |
| QBE | Quattro Pro Saved Query |
| QBF | QuickBASIC Font File |
| QBI | Quickbooks Crash Roll Back File (Intuit, Inc.) |
| QBL | Business Lawyer Document |
| QBO | dBASE IV Ordered Query |
| QBS | Quick Basic Program File (Microsoft) |
| QBW | QuickBooks Primary Data File (Intuit, Inc.) |
| QBW | Quicken File |
| QBX | QuickBooks Accountant Transfer File (Intuit) |
| QC | Quake-C Source Code File (id Software) |
| QC | Steam Source SDK Model Source File (Valve Corporation) |
| QCB | Combat Flight Simulator Quick Combat Editor File (Microsoft) |
| QCB | QConBridge |
| QCC | QC-CALC File |
| QCC | QUCM Firmware Upgrade |
| QCD | Cliq Accessories Phonebook Data |
| QCD | QuarkCopyDesk SE |
| QCF | Q-emuLator |
| QCF | QuickLogic Constraint File |
| QCF | Miliki Super Compressor Pro QuikCAT Compressed File (QuikCAT Technologies) |
| QCH | Quicken for DOS ver 2 Data File |
| QCH | SSI Dark Queen of Krynn File |
| QCI | Cliq Accessories Phonebook Index |
| QCI | Massively Parallel Quantum Chemistry Program File |
| QCK | Jigsaw 2 Astrological Tool File |
| QCK | Quick Charts File |
| QCK | Quick Foram Count File |
| QCK | QuickCard File |
| QCK | VAX CRYSTALS Chemical Crystallogaphy File |
| QCM | 3164 Emulator Quick Command File |
| QCM | QUCM Application File |
| QCP | PureVoice File (Qualcomm) |
| QCS | CADQC Standard File |
| QCT | Memory-Map File |
| QD | SHARP MZ-series Emulator File |
| QD0 | Omnis Quartz Data File Segment 10 |
| QD1 | Omnis Quartz Data File Segment 10 |
| QD2 | Omnis Quartz Data File Segment 2 |
| QD3 | Omnis Quartz Data File Segment 3 |
| QD3 | QuickDraw 3D Metafile |
| QD3D | QuickDraw 3D Metafile |
| QD4 | Omnis Quartz Data File Segment 4 |
| QD5 | Omnis Quartz Data File Segment 5 |
| QD6 | Omnis Quartz Data File Segment 6 |
| QD7 | Omnis Quartz Data File Segment 7 |
| QD8 | Omnis Quartz Data File Segment 8 |
| QD9 | Omnis Quartz Data File Segment 9 |
| QDA | KaleidaGraph Data File (Synergy Software) |
| QDAT | QuickTime Installer Cache (Apple Computer, Inc.) |
| QDB | Quicken Data File Backup (Intuit Inc.) |
| QDB | CUEcards (Marcus Humann) |
| QDF | Quicken Windows Data File (Intuit Inc.) |
| QDF | Label Matrix Bar Code Label (Teklynx Software Solutions) |
| QDF | Snapform Form Document (Ringler Informatik AG) |
| QDI | Dictionary |
| QDI | Quicken Data File |
| QDK | Quarterdeck QEMM File |
| QDP | MPQDraft Plug-in |
| QDP | KaleidaGraph Plot File (Synergy Software) |
| QDT | QuarkXpress Dictionary File (Quark, Inc.) |
| QDT | Question Mark Desigener Test File |
| QDT | QuickBooks UK Accountancy Data File (Intuit, Inc.) |
| QDT | Quicken Data File |
| QDV | Random Dot Software QDV Graphic |
| QDV | Steve Blackstock Giffer Graphics File |
| QE4 | Kingpin Project File |
| QEF | Excel Query (Microsoft) |
| QEL | Quicken Electronic Library File |
| QEM | Expensable Report |
| QEP | IRMA Wordstation for Windows |
| QES | EpiData Questionnaire File (EpiData Association) |
| QEX | ExpensAble Data File |
| QF | Qompose HTML Template (Wade Bowmer) |
| QF | Dispatch Qantas Itinerary Manager Timetable Export File (Scott Andrew Borton) |
| QF | FORTRAN Embedded QUEL |
| QF | Query Filter |
| QFC | QuickFileCollection Archive |
| QFI | Quicken 2002 File |
| QFI | QuickTime Image (Apple Computer, Inc.) |
| QFL | Family Lawyer Document |
| QFN | QuickTime Font File (Apple Computer, Inc.) |
| QFS | Need for Speed Compressed Image (Electronic Arts, Inc.) |
| QFX | Quick Link/Quick Link II Fax |
| QFX | Quicken Transfer File (Intuit Inc.) |
| QIC | Windows Backup Backup Set (Microsoft Corporation) |
| QIF | Quicken Interchange Format (Quicken) |
| QIF | QuickTime Image (Apple Computer, Inc.) |
| QIF | DESQview Compressed Font Archive (Symantec) |
| QIN | Quinnsoft MP3 Player Data File (Quinnsoft) |
| QIP | DESQview Compressed Program Archive (Symantec) |
| QIX | Quicken for DOS ver 2 Data File |
| QIZ | Minimouse's Quiz File |
| QIZ | Quizzical Test |
| QKT | Works (Microsoft) |
| QL$ | MS Compressed QLB |
| QLB | C and QuickBasic-DOS and Visual Basic Quick Library (Microsoft) |
| QLC | PostScript Help File |
| QLC | Type Manager ATM Type 1 Font Script (Adobe) |
| QLE | QOOLE |
| QLF | Family Tree Maker Genealogy File |
| QLP | QuickLink Printer Driver |
| QM | Quality Motion Streaming Video File (KDDI R&D Labs. Inc.) |
| QM2 | Dragon Raja Character File (E-Sofnet Products, Inc.) |
| QM4 | QMail Mail Door Option or Services File |
| QMA | Qedit File |
| QMD | Quicken for Windows ver 5,6 Data File |
| QME | Win3 Quicken Windows File |
| QMF | Lotus Approach Database Query |
| QML | Quicken for DOS ver 2 Data File |
| QMP | SeeYou Raster Maps (Naviter) |
| QMR | OzWin CompuServe E-mail/Forum Access Quickscan History |
| QMT | Quicken Memory List |
| QN2 | QuickNote File |
| QNA | High ASCII Quake Name Maker |
| QNC | Cliq Accessories Notepad Customization |
| QND | Cliq Accessories Notepad Data |
| QNI | Cliq Accessories Notepad Index |
| QNM | High ASCII Quake Name Maker |
| QNT | Chromeleon Quantification Method |
| QNX | Quicken Indexes |
| QPB | Quicken Payroll File (Intuit) |
| QPC | KaleidaGraph Plot File (Synergy Software) |
| QPD | QP Software Dynamic Plug-in |
| QPD | Win3 Quicken Windows File |
| QPD | Qualified Plan Distribution and Tax Analysis System (QPDS) (DATAIR Employee Benefit Systems, Inc.) |
| QPH | Quicken Price History File (Intuit, Inc.) |
| QPI | Win3 Quicken File |
| QPL | KaleidaGraph Layout File (Synergy Software) |
| QPP | QPresenter & Qpresenter Pro Presentation File (Digital Image LLP) |
| QPR | Dinkum Embedded C++ Abridged Library |
| QPR | Foxpro Relational Query (Microsoft) |
| QPR | OS/2 Printer Queue Driver |
| QPS | QP Software Application File |
| QPW | Quattro Pro Project File (Corel Corporation) |
| QPX | Foxpro Ordered Query (Microsoft) |
| QPX | QuickTime Player Plug-in (Apple Computer, Inc.) |
| QQT | Quick Qard Technology Qardware Definition File |
| QR2 | Delphi Database Quick Report File (Borland Software Corporation) |
| QRC | Qt Resource Collection File (Trolltech) |
| QRD | BI/Query Query Result |
| QRF | Questions-Réponses Quiz File (Thomas and Mathieu DUABELE) |
| QRP | Gupta Report Builder File |
| QRP | Dosh Software File |
| QRP | DR Hardware File |
| QRP | Liberty for Windows Report File |
| QRP | COW2000 Report (Software Exception) |
| QRP | QuickReport Report (QuSoft) |
| QRS | WordPerfect Equation Editor (Corel Corporation) |
| QRS | SlickRun MagicWord Pack (Bayden Systems) |
| QRT | QRT Ray Tracing Graphic |
| QRY | BI/Query Query |
| QRY | dBASE IV Query |
| QRY | Lotus Approach Query for SQL Tables |
| QRY | Query (Microsoft) |
| QRY | Query |
| QS9 | OzWin CompuServe E-mail/Forum Access Scan Result File |
| QSA | Encrypted QSA Specifications Database Export File |
| QSC | KaleidaGraph Script File (Synergy Software) |
| QSC | Pxyl Visuals Chart |
| QSD | Quicken for Windows Data File |
| QSF | Micrografx QuickSilver Compressed Internet Live Graphic |
| QSF | Millennium 3 Quick Start File |
| QSF | Quintessential Player Family Skin (Quinnware) |
| QSG | Quest Saved Game (Axe Software) |
| QSK | Quintessential Player Skin (Quinnware) |
| QSL | OzWin CompuServe E-mail/Forum Access Forum Quickscan List |
| QSL | Questionnaire Specification Language File |
| QSM | QuadriSpace Model Format File |
| QSN | TAPCIS QuickScan Data |
| QST | Ami Pro QuickStart Tutorial Image (IBM) |
| QST | KaleidaGraph Style File (Synergy Software) |
| QST | Quake Spy Tab File |
| QST | Zelda Classic Quest (Armageddon Games) |
| QSXL | QuickLayout Session Data (Advanced Publishing Systems Pty Ltd) |
| QT | QuickTime Movie (Apple Computer, Inc.) |
| QTA | qtar Archive |
| QTC | Incite Media Assistant File |
| QTC | QuickTime Ver 2.0+ Windows CODEC (Apple Computer, Inc.) |
| QTCH | Quicktime Cached File (Apple Computer, Inc.) |
| QTE | Questionnaire Specification Language File |
| QTF | Qtracker Filter |
| QTI | QuickTime Image (Apple Computer, Inc.) |
| QTIF | QuickTime Image (Apple Computer, Inc.) |
| QTK | Apple Quicktake (Apple Computer, Inc.) |
| QTL | QuickTime Movie (Apple Computer, Inc.) |
| QTL | YUV SECAM or PAL image |
| QTM | QuickTime Movie (Apple Computer, Inc.) |
| QTMP | Qtracker Mapshot Pack |
| QTN | Norman Virus Control Quarantine File (Norman) |
| QTP | Astra Quicktest Report |
| QTP | QuickTime Preferences (Apple Computer, Inc.) |
| QTPF | QuickTime PreFlight Text (Apple Computer, Inc.) |
| QTPP | Qtracker Program Package |
| QTR | QuickTime Resource File (Apple Computer, Inc.) |
| QTS | Macintosh PICT Image |
| QTS | QuickTime System File (Apple Computer, Inc.) |
| QTSK | Qtracker Skin |
| QTV | QuickTime Virtual Reality Movie (Apple Computer, Inc.) |
| QTVR | QuickTime VR (Apple Computer, Inc.) |
| QTW | QText File |
| QTX | Qtext Text File |
| QTX | Quicken Data File |
| QTX | QuickTime Ver 3/4 Windows CODEC (Apple Computer, Inc.) |
| QTZ | QuaSZ Texture File (Mystic Fractal) |
| QTZ | Quartz Composer Data (Apple Computer, Inc.) |
| QUB | Qubus (KPMG) |
| QUE | CuteFTP Queue File |
| QUE | Task Scheduler Queue Object |
| QUE | SurveySolutions Questionnaire (Perseus Development Corporation) |
| QUE | Sphinx Questionnaire (Le Sphinx Développement) |
| QUI | Brain Quiz File |
| QUICKEN | Quicken Spreadsheet |
| QUP | QuickTime Update Package (Apple Computer, Inc.) |
| QUT | IBM Voice Type Language Vocabels File |
| QVD | Quaanta Media Desktop (GalaxyBeing.com) |
| QVM | Quake File |
| QVP | ViewletBuilder Project File (Qarbon, Inc.) |
| QVW | QlikView Document |
| QW | Symantec Q&A Write Program File |
| QW5 | Quicken 5 File |
| QW6 | Quicken 6 File |
| QWB | Money Quotes WriteBack Import File (Microsoft) |
| QWK | QWK Reader Message |
| QWP | Quiptics Puzzle File |
| QX | Quexal Source Code (Stefano Tommesani) |
| QXB | QuarkXpress Books File (Quark, Inc.) |
| QXD | QuarkXpress Document (Quark, Inc.) |
| QXL | QuarkXpress Element Library (Quark, Inc.) |
| QXM | Quexal Macro (Stefano Tommesani) |
| QXP | QuickCreateXP Course Customiser (SanScrip) |
| QXP | QuarkXpress Project (Quark, Inc.) |
| QXT | QuarkXpress Template File (Quark, Inc.) |
| QZB | Quizzical Test |
| QZB | QuaSZ Zbuffer File (Mystic Fractal) |
| QZM | QuizMaster File |