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A fake book is a collection of simplified sheet music (sometimes called fake music or lead sheets) that have been transcribed manually or otherwise copied. The fake book is a central part of the culture of playing music in public, particularly in jazz, where improvisation is particularly valued.

A song in a fake book contains the melody line, basic chords, and lyrics, the minimal information for musicians adept in improvising to make an impromptu arrangement of a song, or "faking it".

Fake books are not intended for novices: the reader must follow and interpret the scant notation. For someone playing music as a hobby, fake books can be an avenue to playing songs very quickly; a few chords and a one-note melody line can allow an amateur to play a passable version of any song with surprising ease.

Despite the name, fake books are often a thick, loose stack of unbound sheets.

The origins of transcriptions were often murky and not always of the best musical quality. But the sheer amount of the tunes more than compensated for this drawback, especially since skilled musicians could always improve the sound. At some point, there came The Real Book, which claimed to fix all problems of poor design. It was extremely popular and in its turn spawned a number of "fake Real Books". The 6th Edition of the 'Real Book' is legally published (unlike previous versions) and is the most popular fake book ever made.

Fake books originally infringed copyrights, and their circulation was primarily underground. Today, legal versions of fake books can be found in many music stores