File extensions start with character 'M'
| File Type | Category | File Format | |
|---|---|---|---|
| .m | Development Files | Objective-C Implementation File | |
| .m2ts | Video Files | Blu-ray BDAV Video File | |
| .m3d | CorelDRAW Files | 3D Model File | |
| .m3u | Playlist Files | Media Playlist File | |
| .m4a | MPEG Files | MPEG-4 Audio File | |
| .m4b | Audio Files | MPEG-4 Audio Book File | |
| .m4r | Apple Files | iPhone Ringtone File | |
| .macbin | Data Files | Macbinary Encoded File | |
| .maf | Data Files | Mutation Annotation Format File | |
| .maff | Web Files | Mozilla Archive Format File | |
| .mag | Partially Downloaded Files | Access Diagram Shortcut File | |
| .mai | Data Files | Microsoft Mail File | |
| .man | Text Files | Unix Manual | |
| .mani | Digital Video Files | Mine-imator Project File | |
| .manifest | Windows System Files | Windows Application Manifest File | |
| .map | Game Files | Quake Engine Map File | |
| .mar | Partially Downloaded Files | Mozilla Archive | |
| .mart | eBook Files | MartView eBook File | |
| .mas | Game Files | rFactor Track File | |
| .mat | Data Files | MATLAB MAT-File | |
| .mbb | Partially Downloaded Files | Kodak EasyShare Data File | |
| .mbd | Data Files | Multimedia Builder Project File | |
| .mbf | Backup Files | Microsoft Money Backup File | |
| .mbg | Data Files | Mailbag Assistant Mailbox File | |
| .mbk | Backup Files | dBASE IV Multiple Index Backup File | |
| .mbl | Data Files | Logger Pro Data File | |
| .mbox | Text Files | E-mail Mailbox File | |
| .mbp | eBook Files | Mobipocket Notes File | |
| .mbx | Data Files | Outlook Express Mailbox | |
| .mc1 | Data Files | MedCalc Data File | |
| .mca | Game Files | Minecraft "Anvil" Map File | |
| .mcd | Data Files | Mathcad Document | |
| .mcdx | Document Files | Mathcad Prime Document | |
| .mcr | Program Execution Files | 3ds Max Macroscript File | |
| .mcxe | Data Files | MedicinesComplete Data File | |
| .md | Development Files | Markdown Documentation File | |
| .md0 | Disk Image Files | Alcohol Disk Image Segment 1 | |
| .md5 | Multiple Use Files | MD5 Checksum File | |
| .md8 | Data Files | Mediator Project File | |
| .mdb | Microsoft Access Files | Microsoft Access Database | |
| .mdc | Data Files | Multi Dimension Cube File | |
| .mddata | Backup Files | iPhone Backup File | |
| .mde | Microsoft Access Files | Compiled Access Add-in File | |
| .mdf | Disk Image Files | Media Disc Image File | |
| .mdi | Page Layout Files | Microsoft Document Imaging File | |
| .mdl | 3D Model Files | MathWorks Simulink Model | |
| .mdl | Game Files | Half-Life Model File | |
| .mdm | Data Files | HLM Multivariate Data Matrix File | |
| .mdmp | Windows System Files | Windows Minidump | |
| .mds | Disk Image Files | Media Descriptor File | |
| .mdt | Database Files | GeoMedia Access Database Template | |
| .mdx | Disk Image Files | Extended Media Descriptor File | |
| .mdx | 3D Graphics Files | Warcraft 3 Model File | |
| .mdz | Data Files | Access Wizard Template | |
| .me | Configuration Files | Readme Text File | |
| .meg | Data Files | MEGA Data File | |
| .mell | Text Files | Mellel Word Processing File | |
| .mellel | Text Files | Mellel Word Processing Document | |
| .mem | Backup Files | FoxPro Variable File | |
| .menc | Data Files | Windows Mobile Encrypted File | |
| .merlin2 | Data Files | Merlin Project File | |
| .met | Data Files | eMule Resource File | |
| .mex | Data Files | Macro Express File | |
| .mf | Development Files | Java Manifest File | |
| .mfa | Development Files | Multimedia Fusion Development File | |
| .mfe | Data Files | MobileFrame Enterprise Data File | |
| .mfp | Data Files | Macromedia FlashPaper Document | |
| .mft | Page Layout Files | MediaFACE Project Template | |
| .mfu | Data Files | MobileFrame Update File | |
| .mfv | Data Files | MobileFrame Device Pack File | |
| .mgc | Vector Graphics Files | Microsoft Clip Organizer Media Catalog | |
| .mht | HTML Files | MHTML Web Archive | |
| .mindnode | Data Files | MindNode Document | |
| .mint | Compressed Files | Linux Mint Installer File | |
| .mission | Data Files | MissionMaker Project File | |
| .mit | Data Files | MineEdit Inventory Template File | |
| .mix | Raster Graphics Files | Microsoft Image Exchange File | |
| .mjp | Digital Video Files | MJPEG Video File | |
| .mkv | Digital Video Files | Matroska Video File | |
| .mls | Data Files | Milestones Simplicity File | |
| .mm | Development Files | Objective-C++ Source File | |
| .mm6 | Data Files | Money Manager 6 File | |
| .mma | Data Files | Master Album Maker Photo Album File | |
| .mmc | Data Files | Microsoft Media Catalog | |
| .mmf | Audio Files | Synthetic Music Mobile Application File | |
| .mmip | Plug-in Files | MediaMonkey Installation Package | |
| .mml | Page Layout Files | FrameMaker Maker Markup Language File | |
| .mmm | Audio Files | Music Maker Arrangement File | |
| .mmp | Configuration Files | Symbian Project Specification File | |
| .mmu | Data Files | myPM Merge Data File | |
| .mmw | Data Files | AceMoney Money File | |
| .mnc | Data Files | My Notes Center Notebook | |
| .mng | Raster Graphics Files | Multiple Network Graphic | |
| .mnk | Data Files | My Notes Keeper Notebook | |
| .mno | Data Files | Macromedia Design Note | |
| .mnt | Text Files | FoxPro Menu Memo | |
| .mnv | Digital Video Files | PlayStation Movie File | |
| .mny | Data Files | Microsoft Money File | |
| .mo? | Development Files | Machine Object File | |
| .mob | Video Files | MOBTV Video File | |
| .mobi | eBook Files | Mobipocket eBook | |
| .mod | MPEG Files | Amiga Music Module File | |
| .moho | Data Files | Anime Studio Animation Project | |
| .mol | Data Files | MDL Molfile | |
| .money | Data Files | Money Data File | |
| .mos | Camera Photo Files | Leaf Camera RAW File | |
| .mosaic | Data Files | MacOSaiX Mosaic File | |
| .mou | Compressed Files | WinMount Compressed File | |
| .mov | Digital Video Files | Apple QuickTime Movie | |
| .mox | Data Files | ExtendSim Simulation Software Model | |
| .mp3 | Compressed Audio Files | MP3 Audio File | |
| .mp4 | Digital Video Files | MPEG-4 Video File | |
| .mpd | Database Files | Microsoft Project Database | |
| .mpg | Digital Video Files | MPEG Video File | |
| .mpi | Data Files | InstallJammer Project File | |
| .mpj | Data Files | RoboHelp HTML Project | |
| .mpkg | Compressed Files | Meta Package File | |
| .mpo | Raster Graphics Files | Multi Picture Object File | |
| .mpp | Data Files | Microsoft Project File | |
| .mpq | Game Files | Blizzard Mo'PaQ File | |
| .mpr | Development Files | FoxPro Generated Menu Program | |
| .mps | Data Files | Mathematical Programming System File | |
| .mpt | Data Files | Microsoft Project Template | |
| .mpv | Video Files | MPEG Elementary Stream Video File | |
| .mpx | Data Files | Microsoft Project Exchange File | |
| .mpz | Data Files | Miradi Project File | |
| .mpzip | Data Files | Multisim Pack File | |
| .mq4 | Data Files | MetaTrader Custom Indicator | |
| .mqo | 3D Image Files | Metasequoia Document | |
| .mrt | Development Files | Stimulsoft Report File | |
| .ms10 | Data Files | Multisim 10 Circuit Design File | |
| .ms8 | Data Files | Multisim 8 Circuit Design File | |
| .msb | Data Files | Oracle Binary Message File | |
| .msc | System Files | Microsoft Management Console Snap-in Control File | |
| .mse | Encrypted Files | 3ds Max Encrypted MAXScript File | |
| .msf | Multiple Use Files | Mail Summary File | |
| .msg | Email Message Files | Outlook Mail Message | |
| .msi | Multiple Use Files | Windows Installer Package | |
| .msm | Configuration Files | Windows Installer Merge Module | |
| .mso | Multiple Use Files | Inline E-mail Attachment | |
| .msp | System Files | Windows Installer Patch | |
| .mss | Development Files | Microprocessor Software Specification File | |
| .mst | Configuration Files | Windows Installer Setup Transform File | |
| .msu | Partially Downloaded Files | Windows Vista Update Package | |
| .mswmm | Digital Video Files | Windows Movie Maker Project | |
| .mtf | Configuration Files | Motorola Theme File | |
| .mth | Data Files | Derive Math File | |
| .mtm | Audio Files | MultiTracker Module | |
| .mts | Digital Video Files | AVCHD Video File | |
| .mtt | Data Files | MetadataTouch Template | |
| .mtw | Data Files | Minitab Worksheet File | |
| .mtz | Compressed Files | MIUI Theme | |
| .mtz | 3D Graphics Files | Compressed MetaStream Scene File | |
| .mu | Quattro Pro Files | Kerbal Space Program Mesh File | |
| .muf | Data Files | Alpha Five Licence File | |
| .mui | Windows System Files | Multilingual User Interface File | |
| .mup | Data Files | Music Publisher Score | |
| .mus | Audio Files | Finale Notation File Format | |
| .mw | Data Files | Maple Worksheet | |
| .mwd | Text Files | MarinerWrite Document | |
| .mwf | Data Files | MapGuide Author Map Window File | |
| .mwp | Text Files | Lotus Word Pro SmartMaster File | |
| .mws | Document Files | Maple Classic Worksheet | |
| .mwx | GIS Files | MapGuide Author Map Window XML File | |
| .mx | Data Files | Mathematica Serialized Package File | |
| .mxad | Data Files | Mandelbrot Explorer All Data File | |
| .mxc2 | Data Files | MAGIX Cache File | |
| .mxi | Raster Graphics Files | Maxwell Image | |
| .myi | Data Files | MySQL MyISAM Index File | |
| .mys | Digital Video Files | Vineyard Captured Video File | |
| .mzz | Partially Downloaded Files | Microsoft .NET Download Package |