| lsk | Liskell Source Code |
| lsl | Altium Designer Linker Script |
| lsp | Lisp Source Code |
| lss | LotusScript Source Code |
| lss | GCC Assembler Listing File |
| lst | GCC Assembler Listing File |
| ltb | LithTech Binary File |
| lua | LUA Source Code |
| lub | LUA Binary |
| luc | LuaTeX Compiled LUA Script |
| luci | LuCI Script |
| lvm | LabVIEW Measurement |
| lvr | Microsoft Test Manager Link |
| lxb | LXBatch Program |
| lxp | LXP Source Code |
| m | MATLAB Script |
| m1s | Mach3 Macro |
| m3 | Modula-3 Source Code |
| m4 | M4 Macro File |
| m4m | SynDEx Makefile Macro |
| m4x | SynDEx Executive Macro |
| m6m | Mazatrol M640M NC Unit |
| mac | UltraEdit Macro |
| magik | Magik Source Code |
| mak | Visual Studio Makefile |
| make | Xcode Make File |
| mako | Mako Template |
| manifest | Java Manifest File |
| markdn | Markdown Document |
| markdown | Markdown Document |
| master | ASP.NET Master Page |
| mat | MATLAB Matrix |
| matlab | MATLAB Script |
| maz | Mazatrol Program |
| mbac | MascotCapsule Resource Data |
