G7b9

G7b9 is a dominant seventh chord built on the note G with a lowered ninth, typically written as G-B-D-F-Ab. The b9 is the Ab above G (enharmonically equivalent to G#). As an altered dominant, G7b9 functions to heighten tension before resolving to a tonic chord, most commonly C major or C minor, in tonal music.

The chord’s defining features are the major triad (G-B-D), the minor seventh (F), and the lowered ninth (Ab). The presence of Ab adds dissonance beyond a standard G7, intensifying the pull of the dominant to the tonic. In harmonic practice, tensions such as the b9 are resolved by stepwise motion to tones in the target chord, while the B–F tritone maintains a strong dominant character.

In performance and analysis, G7b9 is often used in jazz, pop, and film music to create a sense of forward motion toward the tonic. It frequently appears in progressions such as V7b9 → I, and can be combined with other alterations (for example, #5 or natural 11) as part of the V7alt family. Voicings vary: in four-note chords, players may omit the root and place the B, F, and Ab (and sometimes D) in the upper voices; inversions of the chord place different chord tones in the bass.

See also: altered dominant chords, V7alt, tritone substitution. The chord is denoted as G7(b9) in most analyses and scores.