A head theme framework for a jazz improviser is a simple AA or AABA song form. In many cases a composer of the particular theme is not a jazz musician himself and a jazz performer tends to introduce stylistic modifications which sometimes threaten to change the original character. Thanks to the extraordinary individual recordings some themes had become 'standards' which later kept evolving through the generations until the mid sixties. A ballad is an obligatory part of every jazz concert and jazz record, in the case of ballads a jazz musician is interested mainly in harmonic improvements fitting the rules of jazz language, rather than melody itself connected to the lyrics, Johnny Green s ballad 'Body And Soul' became the tenor saxophone standard as a result of Coleman Hawkins' recording from 1939 in which Hawkins had introduced for the first time a tritone substitution for a dominant chord. John Coltrane completed harmonic changes of this ballad in 1960 involving his 'Coltrane Changes' By introducing the row of four descending II-V7 chords Dizzy Gillespie refreshed a single key harmonic stereotype in trumpet ballad 'I Can't Get Started' in 1945. Richard Rodgers' ballad 'My Funny Valentine' has been a subject of evolution in several Miles Davis' recordings from 1956 until 1964 when he at the end insisted upon modal treatment of one part of this song. Bud Powell has set the harmonic background for Harold Arlen's Academy Award ballad 'Over The Rainbow' beginning the song with #IV half diminished chord instead of I maj7, and with II-V7 tritone substitution in the second bar. Jazz musicians have been composing mainly instrumental ballads and vocalists would be adding on lyrics with the risk of lowering the artistic quality, as has happened to the Thelonious Monk's 'Round About Midnight'. A good interpretation of a ballad in jazz is gradually reached with maturing of one's musical personality.