| 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 |
| ll3 | LapLink 3 Data |
| lla | PROJ.4 LLA Data |
| llc | LapLink Saved Connection Data |
| lld | Loan Level Disclosure Data |
| llge | Microsoft Windows Application Log |
| lli | Autodesk AutoCAD Landscape Library |
| llog | Legit Log Viewer Log Data |
| llt | Liquidity Lighthouse Transaction Data |