Ii-V-I turnaround

The ii–V–I progression (occasionally referred to as ii–V–I turnaround, and ii–V–I) is a common cadential chord progression used in a wide variety of music genres, including jazz harmony. It is a succession of chords whose roots descend in fifths from the second degree (supertonic) to the fifth degree (dominant), and finally to the tonic. In a major key, the supertonic triad (ii) is minor, and in a minor key it is diminished. The dominant is, in its normal form, a major triad and, commonly, a dominant seventh chord. With the addition of chord alterations, substitutions, and extensions (most often sevenths), limitless variations exist on this simple formula.

ii–V–I has been used for years and is currently "a staple of virtually every type of popular music," including jazz, R&B, pop, rock, and country. Examples include "Honeysuckle Rose" (1928), which, "features several bars in which the harmony goes back and forth between the II and V chords before finally resolving on the I chord," and "Satin Doll" (1953), and "If I Fell".

ii–V–I progressions are extremely common in jazz. They serve two primary functions, which are often intertwined: to temporarily imply passing tonalities, and to lead strongly toward a goal (the "I" chord). One potential situation where ii-V-I progressions can be put to use is in a blues, whose generic form has no such progressions. In this example, a simple 12-bar F blues is shown followed by a similar one with some basic ii–V–I substitutions (in bold):

In bar 4, instead of the simple V I root motion in the original blues, the ii chord of the B♭7 (Cm) is included so that the measure is even more directed toward the following downbeat with the B♭7. In bars 8-10, instead of leading back to the tonic with the standard V–IV–I (blues cadence), a series of applied ii–V–I progressions is used to first lead to Gm, which then itself is reinterpreted as a ii and used to lead back to F7 through its own V, which is C7. In the last bar (the "turnaround"), the same type of substitution is used as that in bar 4. In practice, musicians often extend the basic chords shown here, especially to 7ths, 9ths, and 13ths, as seen in this example:

...
Wikipedia