A-flat major is a major scale based on A♭, with the pitches A♭, B♭, C, D♭, E♭, F, and G. Its key signature has four flats.

The A-flat major scale is:

Changes needed for the melodic and harmonic versions of the scale are written in with accidentals as necessary. The A-flat harmonic major and melodic major scales are

Its relative minor is F minor. Its parallel minor, A-flat minor, is usually written instead as the enharmonic key of G-sharp minor, since A-flat minor, which contains seven flats, is not normally used. Its enharmonic, G-sharp major, with eight sharps, including the F, has a similar problem, and so A-flat major is often used as the parallel major for G-sharp minor. (The same enharmonic situation also occurs with the keys of D-flat major and C-sharp minor, and to some extent, the keys of G-flat major and F-sharp minor).)

The scale degree chords of A-flat major are:

Beethoven chose A-flat major as the key of the slow movement for most of his C minor works, a practice which Anton Bruckner imitated in his first two C minor symphonies and also Antonín Dvořák in his only C minor symphony. The second movement of Haydn's 43rd symphony in E-flat major is in A-flat major. Frédéric Chopin used this key in many of his works, particularly in his waltzes.

Since A-flat major was rarely chosen as the main key for orchestral works of the 18th century, passages or movements in the key often retained the timpani settings of the preceding movement. For example, Beethoven's Symphony No. 5 has the timpani set to C and G for the first movement. With hand-tuned timpani, there is no time to re-tune the timpani to A-flat and E-flat for the slow second movement in A-flat major; accordingly, the timpani in this movement are reserved for the passages in C major. In Bruckner's Symphony No. 1 in C minor, however, the timpani are re-tuned between the first movement in C minor and the following in A-flat major.

Charles-Marie Widor considered A-flat major to be the second best key for flute music.