ii–V–I

The ii–V–I is the central harmonic progression of jazz. In the key of C major, it is Dm7–G7–Cmaj7: a minor seventh chord on the second scale degree, a dominant seventh chord on the fifth, and a major seventh chord on the tonic. Nearly every jazz standard is built from chains and variants of ii–V–I progressions, and learning to navigate them is the fundamental skill of jazz harmony.

The progression's power comes from the tritone embedded in the dominant seventh chord. In G7, the third (B) and seventh (F) are a tritone apart. This interval is maximally unstable and resolves outward by half step: B moves up to C and F moves down to E, landing on the root and third of the Cmaj7 chord. This voice leading is so strong that the ear expects resolution even when it is denied or delayed.

Each chord in the ii–V–I has a characteristic scale. The ii7 chord (Dm7 in C) is harmonized with the Dorian mode (D–E–F–G–A–B–C), which supplies a natural sixth and a minor seventh. The V7 chord (G7) is harmonized with the Mixolydian mode (G–A–B–C–D–E–F), which supplies the characteristic minor seventh of a dominant chord. The Imaj7 chord (Cmaj7) uses the Ionian mode (the major scale). Jazz improvisers learn to shift scales smoothly through these three chords, giving each a distinct sound while maintaining melodic continuity.

In minor keys, the ii–V–I is spelled iim7♭5–V7–Im7: a half-diminished chord, an altered or Phrygian-dominant V7, and a minor tonic. The tension is even greater because the V7 chord often carries additional alterations (♭9, ♯9, ♭13). Recognition of ii–V–I patterns — both major and minor — in real time is considered the cornerstone of jazz ear training.