The Long Filename interface enables access to files with names that do not fit the MS-DOS standard filenaming convention on network drives. The following list outlines these functions, and provides a brief description of each.
| Function | Description |
| LFNFindFirst | Searches for the first file with a matching name. |
| LFNFindNext | Searches for the next file with a matching name. |
| LFNFindClose | Ends the search for matching files. |
| LFNGetAttributes | Retrieves file attributes. |
| LFNSetAttributes | Sets file attributes. |
| LFNCopy | Copies a file. |
| LFNMove | Moves a file. |
| LFNDelete | Deletes a file. |
| LFNMKDir | Creates a directory. |
| LFNRMDir | Removes a directory. |
| LFNGetVolumeLabel | Retrieves the volume label. |
| LFNSetVolumeLabel | Sets the volume label. |
| LFNParse | Parses paths. |
| LFNVolumeType | Specifies volume type. |
Typically, these functions are called only when a network drive with long filenames is detected. In other words, they do not need to support local drives. The exception is the LFNCopy function which must be able to copy to or from any type of volume.
The return value is typically an MS-DOS error function (as returned from MS-DOS functions when the carry flag is set, or from Interrupt 21h Function 59h, Get Extended Error Information). If a function returns the special error code 0xFFFF, then the network error message functions will be called to retrieve error message text.
The maximum length of any long filename will be assumed to be 260 characters, including the terminator.
File-attribute values are identical to MS-DOS file-attribute fields.