Cool jazz is a style of jazz music that arose during the Second Worl'''d War. During this time, there was an influx of Californian (predominantly white) jazz musicians to New York. Once there, these musicians mixed with the mostly black bebop musicians, and were also influenced by the "smooth" sound of black saxophonist Lester Young. The style that emerged became known as "cool jazz", which avoided the aggressive tempos of bebop. Cool jazz included intricate arrangements, innovative forms, and songs having a thoroughly composed sound (although they included improvised sections). The term "cool" started being applied to this music about 1953 with the release of the album Classics in Jazz: Cool and Quiet by Capitol Records^[1].

Cool jazz had several sources. Arrangers Gil Evans and Gerry Mulligan developed their initial ideas working for the Claude Thornhill Orchestra, which featured such then-unheard-of instruments (for jazz) as french horn and tuba; the added forces permitted Evans and Mulligan to explore softer emotional and timbral shading than had been typical of swing-era big bands. Another variety of "cool jazz" was that of the pianist Lennie Tristano and his students, notably the saxophonists Lee Konitz (who spent some time in the Thornhill band) and Warne Marsh. Tristano's music is very different from what Evans and his colleagues were doing: its "coolness" was a matter of emotion (Tristano required saxophonists to play with a "pure" tone and to concentrate on melodic development and interaction rather than overt emotionalism), but his emphasis on sometimes ferociously fast tempos and on pure improvisation rather than arrangement was closer to bebop.

The classic mixture of these various influences was during the 1949-1950 sessions now best known under their later title: Miles Davis's Birth of the Cool (1950). Despite Davis's top billing, this was in fact a collective project that drew together many players and arrangers/composers from the period: Davis, Evans, Mulligan, Konitz, John Lewis, Gunther Schuller, and Johnny Carisi, although according to Evans, Miles Davis was the musician who best represented this style of jazz. Issued only shortly after bebop had begun to establish itself, this recording offered an alternative aesthetic that was initially unpopular – it originally sold poorly and the band did not last long – but slowly established itself as a jazz classic.

Despite its beginning in New York, cool jazz later became identified strongly with West Coast jazz. Californian group The Dave Brubeck Quartet recorded the popular Cool Jazz album Time Out in 1959, which scored number two on the Billboard "Pop Albums" chart. The Cool Jazz influence stretches into such later developments as bossa nova, modal jazz (especially in the form of Davis's Kind of Blue 1959), and even free jazz (in the form of Jimmy Giuffre's 1961-1962 trio).

• List of cool jazz and West Coast jazz musicians

• Gioia, Ted, "Cool Jazz and West Coast Jazz", chapter in Kirchner, Bill, The Oxford Companion to Jazz, Oxford University Press US, 2005. ISBN 0195183592
• MacAdams, Lewis, Birth of the Cool: Beat, Bebop, and the American Avant-Garde, Simon and Schuster, 2001. ISBN 0684813548

• A History of Cool Jazz in 100 Tracks, edited by Ted Gioia (Jazz.com)
• allmusic Cool Jazz
• Forever Cool: Cool and West Coast Jazz on the Internet
• The Birth of the Cool 1927, by Len Weinstock.

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