GNU LilyPond is a computer program for music engraving. One of LilyPond's major goals is to produce scores that are engraved with traditional layout rules, reflecting the era when scores were engraved by hand.
Unlike some commercial, proprietary music engraving software, such as Finale and Sibelius, LilyPond does not contain its own graphical user interface for the creation of scores. It does, however, have the same aim of producing output comparable to professionally-engraved scores. Some graphical music notation programs, such as Rosegarden, NoteEdit and Canorus, can export files directly to LilyPond format. LilyPond can also automatically generate MIDI files from music specified in the LilyPond format. The Mutopia project, which distributes free content sheet music, uses LilyPond to typeset its music, as does Musipedia, a collaborative music encyclopedia. WikiTeX, a MediaWiki interface, supports editing LilyPond notation directly in wiki articles.
LilyPond is cross-platform, and is available for several common operating systems; released under the terms of the GNU General Public License, LilyPond is free software.