| lay | Pro/ENGINEER Layout |
| lay | ArchiCAD PlotMaker Layout |
| layout | Adobe Premiere Workspace Layout |
| layx | PTV VISSIM Vehicle Network Data |
| laz | LASzip Compressed Lidar Data |
| lbd | Life Balance Data File |
| lbe | Life Balance XML Exchange Data |
| lbg | dBASE IV Label Generator Data |
| lbk | ArchiCAD PlotMaker Layout Book |
| lbo | dBASE IV Compiled Label |
| lbr | EAGLE Library File |
| lbv | T-Online Ob4hbci Layout Print File |
| lbxcol | Libronix DLS Resource Collection |
| lbxdtp | Libronix DLS Data Type |
| lbxlls | Logos 3 LLS Data |
| lbxoeb | Libronix DLS Resource |
| lc | L0phtCrack Password Database |
| lcb | Kodak EasyShare Album List |
| lcd | Abbyy FineReader Dictionary File |
| lcf | ArchiCAD Library Container File |
| lcl | LISCAD Lite Database |
| lcm | Lipikar Custom Map |
| lcn | Trymedia License Data |
| lcp | FARSITE Landscape Data |
| lcpl | Readium License Document |
| lcs | Light-O-Rama Compressed Sequence File |
| lcs | L0phtCrack Password Database |
| lcs | Alstom MMS LCS Compiler Report |
| lcv | Radio Mobile Land Cover Data |
| lcx | LC Model |
| ld | MoTeC Telemetry Log |
| ld1 | dBASE IV Overlay File |
| ld2 | Lingoes Compiled Dictionary |
| ldata | JSim Line Data Format |
| ldb | Sybase PowerDesigner Logical Data Model Backup |