In music theory, a diminished major seventh chord is a seventh chord composed of a diminished triad and a major seventh.^[1] Thus, it is composed of a root note, together with a minor third, a diminished fifth, and a major seventh above the root: (1, ♭3, ♭5, 7). For example, the diminished major seventh chord built on C, commonly written as C^oM7, has pitches C–E♭–G♭–B:

Diminished major seventh chords are very dissonant, containing the dissonant intervals of the tritone and the major seventh. They are frequently encountered, especially in jazz, as a diminished seventh chord with an appoggiatura^{[citation needed]}, especially when the melody has the leading note of the given chord: the ability to resolve this dissonance smoothly to a diatonic triad with the same root allows it to be used as a temporary tension before tonic resolution. It is nevertheless infrequently used as a chord in itself.

The chord can be represented by the integer notation {0, 3, 6, 11}.