What is a music publisher?

Traditionally, music publishers operate similarly to book publishers, only for music instead of books.  They ensure that the songwriters and composers receive compensation for the use of their music by different entities.  Music publishers usually get a 50% royalty.

The most unscrupulous music publishers are songsharks, who do little if any legal work and they make their profit through the use of various fees.  Those fees are generally for services that are offered by legitimate publishers for no cost as part of the job.