Traditionally – and especially in the classical era – the dominant 7th chord is a V7 chord in a diatonic chord scale that resolves back to the tonic (or I) chord.

In modern music however, our ears are used to hearing the dominant 7th chord function in more ways than just a V7 resolving to a I. In blues and pop music, the dominant seventh chord can be used as the I (or home) chord. This is most evident in the blues, where all three chords are often dominant 7th chords.