While the original, often bootlegged, " Real Book " (now officially published by Hal Leonard) is the standard, many other sources exist:

A popular online resource allowing quick access to hundreds of tunes.

Musicians can carry thousands of tunes on a tablet or phone, eliminating the need to lug heavy binders.

Older "bootleg" PDF versions of the Real Book are notoriously filled with wrong chords or melodies. It is often necessary to check the PDF against a trusted recording.

Finding a tune by title or composer takes seconds rather than minutes.