| ldml | Lasso Dynamic Markup Language Document |
| lds | Binutils Linker Script |
| lds | Liquid Studio Source Code |
| ldx | Liquid Studio Compiled Executable |
| less | LESS Style Sheet |
| lfm | Lazarus Form |
| lg32 | GFA-BASIC 32 Library |
| lgf | ProWorx NXT Log Book Note |
| lgo | Logo Source Code |
| lgt | Logtalk Source Code |
| lhs | Literate Haskell Script |
| lib | ESPL Encrypted Programming File |
| lib | Visual C++ Import Library |
| license | Visual Studio Binary License Data |
| licx | Visual Studio License Text |
| lif | HP-UX LIF File |
| lin | µVision Linker Control Data |
| link | Eclipse Link File |
| linq | LINQPad Source Code |
| lipg | LiPG Parser |
| lis | HP OpenVMS List Data |
| lisp | Lisp Source Code |
| litcoffee | CoffeeScript Literate Script |
| livecode | LiveCode Stack File |
| lkc | LTIB Top Level Config |
| lkf | ST Visual Develop IDE Link Data |
| lkr | MPLAB Linker Data |
| lks | Lookout Direct Source Code |
| llb | LabVIEW Library |
| llf | IITM Local Language File |
| llp | VersaPro Compiled Local Logic Block |
| llx | LabVIEW Virtual Instrument Library Backup |
| lmo | Lua Machine Objects |
| ln | UNIX Lint Data |
| lnp | uVision Linker Input File |