Roy Eldridge in the context of Hipster (1940s subculture)

The tritone substitution is a common chord substitution found in both jazz and classical music. Where jazz is concerned, it was the precursor to more complex substitution patterns like Coltrane changes. Tritone substitutions are sometimes used in improvisation—often to create tension during a solo. Though examples of the tritone substitution, known in the classical world as an augmented sixth chord, can be found extensively in classical music since the Renaissance period, they were not heard outside of classical music until they were brought into jazz by musicians such as Dizzy Gillespie and Charlie Parker in the 1940s, as well as Duke Ellington, Art Tatum, Coleman Hawkins, Roy Eldridge and Benny Goodman.

The tritone substitution can be performed by exchanging a dominant seventh chord for another dominant seventh chord which is a tritone away from it. For example, in the key of C major one can use D♭ instead of G (D♭ is a tritone away from G, and G is the dominant of C).

John Birks "Dizzy" Gillespie (/ɡɪˈlɛspi/ ghih-LES-pee; October 21, 1917 – January 6, 1993) was an American jazz trumpeter, bandleader, composer, educator and singer. He was a trumpet virtuoso and improviser, building on the virtuosic style of Roy Eldridge but adding layers of harmonic and rhythmic complexity previously unheard in jazz. His combination of musicianship, showmanship, and wit made him a leading popularizer of the new music called bebop. His beret and horn-rimmed spectacles, scat singing, bent horn, pouched cheeks, and light-hearted personality have made him an enduring icon.

In the 1940s, Gillespie, with Charlie Parker, became a major figure in the development of bebop and modern jazz. He taught and influenced many other musicians, including trumpeters Miles Davis, Jon Faddis, Fats Navarro, Clifford Brown, Arturo Sandoval, Lee Morgan, Chuck Mangione, and balladeer Johnny Hartman.

The swing era (also frequently referred to as the big band era) was the period (1933–1947) when big band swing music was the most popular music in the United States, especially for teenagers. Though this was its most popular period, the music had actually been around since the late 1920s and early 1930s, being played by black bands led by such artists as Duke Ellington, Jimmie Lunceford, Bennie Moten, Cab Calloway, Earl Hines, and Fletcher Henderson, and white bands from the 1920s led by the likes of Jean Goldkette, Russ Morgan and Isham Jones. An early milestone in the era was from "the King of Swing" Benny Goodman's performance at the Palomar Ballroom in Los Angeles on August 21, 1935, bringing the music to the rest of the country. The 1930s also became the era of other great soloists: the tenor saxophonists Coleman Hawkins, Ben Webster and Lester Young; the alto saxophonists Benny Carter and Johnny Hodges; the drummers Chick Webb, Gene Krupa, Jo Jones and Sid Catlett; the pianists Fats Waller and Teddy Wilson; the trumpeters Louis Armstrong, Roy Eldridge, Bunny Berigan, and Rex Stewart.

Developments in dance orchestras and jazz music culminated in swing music during the early 1930s. It brought to fruition ideas originated with Louis Armstrong, Earl Hines, Fletcher Henderson, Duke Ellington, and Jean Goldkette. The swing era also was precipitated by spicing up familiar commercial, popular material with a Harlem-oriented flavor and selling it via a white band for a white musical/commercial audience. In Benny Goodman's band, the most diversified styles flowed together: the ensemble style developed by Fletcher Henderson, who arranged for Goodman; the riff technique of Kansas City; and the precision and training of many white musicians. On the other hand, the easy melodic quality and clean intonation of Goodman's band made it possible to "sell" jazz to a mass audience.