About the iTunes Library.itl file

This file is a database of the songs in your library and the playlists you've created. Some song-specific data is saved in this file. If you delete the file, iTunes creates a new, empty copy when you open the application, but any playlists, song ratings, comments, or other information is lost. The iTunes Library file is only used by iTunes, and is the only one backed up by Time Machine on OS X.

For iTunes for Mac versions 10.4 and earlier, the library file name was iTunes Library with no file extention.

New versions of iTunes sometimes include enhancements to the iTunes library. When you open the new version of iTunes, iTunes updates your existing library to the new format and places a copy of the old library in the Previous Libraries folder. After iTunes updates successfully to the latest version, you can delete the older iTunes Library files.