"Countdown" is a hardbop[1][2][3][4]jazz standard composed by American jazz saxophonist John Coltrane that was first featured on his fifth studio album, Giant Steps, in 1960. The song is a contrafact of Miles Davis's "Tune Up", which is reharmonized to the Coltrane changes.[3][5] The original recording has been described as having "resolute intensity . . . [that] does more to modernize jazz in 141 seconds than many artists do in their entire careers".[6]
The song is a 16-bar form. Each four bars incorporates the same tonal centers of "Tune Up", which are D major, C major, and B♭ major.
Each tonal center begins with the ii chord but then cycles through two different keys before arriving at the I chord. The ii chord is followed by a dominant 7 chord that is a half step above—using the first four bars as an example, this would be Em7 and F7. This dominant 7 chord resolves in a V-I manner—F7 to B♭Δ7. The next key center is cycled to by playing the dominant 7th chord a minor third up from the last key center—D♭7 to G♭Δ7 to A7 to DΔ7. The next four bars, and new key, starts by making the I chord the ii of the next key.[7]