| lsq | PaleoMag Least Squares Data |
| lsr | LANsurveyor Report |
| lst | Adobe Font List |
| lst | E-Sword v8 Verse List |
| lstx | E-Sword v9 Verse List |
| lsu | LANsurveyor Map |
| lsw | DxLibraryStudio Workspace |
| lsz | Litestep Theme File |
| lt | Moltemplate Data File |
| lt2 | Poser Light Data |
| lta | Monolith LithTech Game Engine Data |
| ltc | Linguistic Tree Constructor Data |
| ltcx | Linguistic Tree Constructor XML Data |
| ltd | LivingTime Data File |
| ltd | HPE Library and Tape Tools Support Ticket |
| ltf | Frogans Short-cut |
| lth | Roxio Label Creator Style Data |
| lthmb | Adobe Presenter Audio Thumbnail |
| ltl | TwoTowers LTL Formula |
| ltn | Carlson Survey Lot Network File |
| ltt | HP Library and Tape Tools Log |
| ltz | Poser Compressed Light Data |
| ltz | Poser Light Data |
| luar | UltraDefrag Lua Report |
| lucy | HTC Scribble Note |
| lud | CARE-S InfoWorks Land Use Data |
| lud | ABBYY Lingvo Dictionary User Dictionary |
| luh | ARINC 615A Load Upload Header |
| lum | Luminous Schedule File |
| lup | OzWin Library Update File |
| lup | ARINC 615A Load Upload Part |
| lus | ARINC 615A Load Upload Status |
| lux | Spectramap Database |
| luz | Spectramap Data |
| lvc | Alstom MMS LVC Compiler Report |