Music publishing is significantly different from the publishing of written creative expression. There are a great many more elements involved in music publishing, and many more channels of publication. Generally speaking, a musician cannot self-publish effectively -- at least, not for a living wage.
The act of publishing music can take several forms. First, there is the songwriting; the basic act of putting the notes (and optionally, lyrics) down in a tangible form such as sheet music. But even written musical notation is not required to create a song; any audible performance of music constitutes a creative expressive even if it is not recorded. Then there is the recorded version of a musical work, which can be copied and distributed. CD albums are what most musicians think of when they think "publishing." But CDs are only a fraction of the music publishing business -- the potential revenue stream.
Publishing also includes concert performances, performances by other artists in innumerable venues ranging from auditoriums to coffee houses, radio and television broadcasts, and -- increasingly -- streaming audio and downloaded MP3 files on the Internet. There are also lucrative rights in the lyrics and musical notation; anyone who publishes the words or notes to a song owes the musician a license fee.
Music publishing companies are organized to manage and promote the publication of a musician's work. Music publishers relieve the artist of the enormous, never-ending tasks of monitoring all the uses of a musical work and collecting license fees for it. They maintain relations with broadcasters, concert organizers, and other venue/medium figures to get the artist's work exposed and played in a profitable manner.
There are two major music publishing companies: BMI and ASCAP. These giant firms are the top-tier clearinghouses for the licensing and collection of royalties for music, musicians, and smaller music publishers. Each has its own way of doing things, and many musicians are affiliated with both.
Smaller music publishers tend to focus on the promotion of music, constantly reaching out to broadcasters and event organizers to get billable play time for the musicians they represent. Many musicians, after successfully publishing a few songs, organize their own music publishing companies and promote the music of newer, less well-known artists.
The contracts involved in music publishing are extremely complex because they involve so many different rights and parties. An attorney expert in music publishing is essential for any artist who plans to publish his or her music.