| lh | LayaAir Sprite3D Data |
| lhp | Lighthouse Organizer Data |
| lhr | Intuit Quicken Financial Life for Mac File |
| li5 | LOGINventory 5 Data |
| lia | P-CAD Schematics Library |
| lib | TINA Library |
| lib | Maple Repository Data File |
| lib4d | Maxon Cinema 4D Preset Library |
| libpkg | Altium Designer Integrated Library Package |
| library | Catia Library |
| library-ms | Windows Library Description |
| lic | General License File |
| lif | Intuit TurboTax Information Archive |
| lig | Afm2pl Ligkern Specifications |
| lij | Apple Photos Data |
| lim | LIMP Impedance Data |
| lims | Liquid Injection Molding Simulation Data |
| lin | Autodesk AutoCAD Linetypes |
| lin | LISCAD Line Styles Data |
| lir | CAP42 License Request File |
| lis | SQR Printer Output |
| lis | Tekla Structures Exported Model |
| list | PLINK Genotype List File |
| lith | DROPS Simulator Lithology Data |
| little | Mozilla Firefox Start-up Cache |
| liv | Living Actor Data File |
| lix | ExtendSim Simulation Software Library |
| ljb | LightJockey Database |
| lk | OpenInsight LK Data |
| lka | Lookout Direct Security Data |
| lko | Microsoft Outlook Express Junkmail Data |
| lkp | Microsoft SMS Lookup File |
| lkt | EES Lookup Table |
| lkup | iiV Lookup |
| ll | List and Label Preview |