The Real Book got its name to distinguish it from the Fake Book which printed only chords and lyrics of standard songs to avoid copyright issues.
The first Real Books included melody lines of jazz standards, thus infringing music copyright, and the older versions were pirated, unlicensed publications that paid no royalties. In 2004, Hal Leonard began publishing the current range of licensed editions, which pays royalties to song authors.
Jazz musicians find it convenient to work from "the book", because it is available in different editions to suit B♭, E♭, and C (concert-pitch) instruments, as well as bass clef and voice editions ("low" and "high" voice, with lyrics included). A band leader can conveniently call out page numbers, since each edition is set out identically. As well as these popular books, Hal Leonard offer other books of jazz standards that cater for all instruments such as the Jazz Play-Along Series which is ideal for learning new repertoire and practicing improvisation.
Whilst being mainly jazz & blues based - the range of Real books extend to other genres too, such as pop & rock, folk and classical.
The Real Book you know and love has now been updated to include rhtyhm band (piano, bass and drums) backing tracks for 240 songs available online for download or streaming! Volume I also now is available in this format.