[1] This composition is in the key of D-flat major but makes extensive use of the secondary dominant chords, secondary ii–V–I progressions, diatonic circle of fifths, and evaded cadences.
[2] The song is extremely chromatic and complex, employing sophisticated mathematics that were rare at this time in jazz:[3] Ellington's rising semitones (G-G#-A-A#-B) at the end of the bridge mirror the opening of both A sections (B-A#-A-G#-G).
Using his fame and artistic freedom, Ellington became more ambitious and experimental, writing "Prelude to a Kiss", which abandoned the Tin Pan Alley style hooks and dance tempo for melodic lines and harmonies found more often in classical music.
[4] He recorded this piece as an instrumental in August 1938 before returning to the studio a few weeks later to record it as a vocal number with lyrics by Irving Gordon and Irving Mills that were sung by a young and relatively unknown Mary McHugh.
[6] Gunther Schuller described "Prelude to a Kiss" as "One of Ellington's finest ballads, although too sophisticated in its weaving melody and chromatic harmonies to gain wide public acceptance.