In jazz and jazz harmony, "rhythm changes" refers to the chord progression occurring in George Gershwin's song "I Got Rhythm". This pattern, "one of the most common vehicles for improvisation," forms the basis of countless (usually uptempo) jazz compositions, was popular with swing-era musicians: It is found in "Shoeshine Boy" (Lester Young's 1936 breakout recording with Count Basie) and "Cotton Tail" written by Duke Ellington in 1940, as well as Charlie Christian's "Seven Come Eleven", Dizzy Gillespie's "Salt Peanuts", and Thelonious Monk's "Rhythm-a-Ning", for instance. The earliest known use of rhythm changes was by Sidney Bechet in his September 15, 1932 recording of "Shag" with his "New Orleans Feetwarmers" group.