West Coast jazz refers to styles of jazz that developed in the American West Coast cities of Los Angeles and San Francisco during the 1950s. West Coast jazz is often seen as a subgenre of cool jazz, which consisted of a calmer style than bebop or hard bop. The music relied relatively more on composition and arrangement than on the individually improvised playing of other jazz styles. Although this style dominated, it was not the only form of jazz heard on the American West Coast.

Before World War II, the west coast of the U.S. hosted a bustling music scene, though its activity remained largely localized. In 1917, Jelly Roll Morton moved to California and remained in Los Angeles until 1922, when he left for Chicago. Kid Ory formed a band in Los Angeles after moving to California in 1919. In 1944, Norman Granz began staging Jazz at the Philharmonic shows at Philharmonic Auditorium in Los Angeles. In 1946, Ross Russell established Dial Records in Hollywood to record Charlie Parker during his sojourn in Los Angeles. Meanwhile, a thriving jazz scene had appeared along Los Angeles's Central Avenue, featuring Dexter Gordon, Wardell Gray, Teddy Edwards, Charles Mingus, and Buddy Collette. Central Avenue's activity rivaled that of the earlier Kansas City jazz scene, but at the time it was little-known outside Los Angeles.

In 1947, Woody Herman organized a new band, the Second Herd, in Los Angeles. The group included tenor saxophonists Stan Getz, Zoot Sims, and Herbie Steward, and baritone saxophonist Serge Chaloff. The resulting "Four Brothers" sound (named for the Jimmy Giuffre composition, "Four Brothers," which highlighted this group) was a precursor of the cool style.

In 1949–1950 baritone saxophonist Gerry Mulligan participated in the Miles Davis band, contributing arrangements to the recordings that became Birth of the Cool (1957). In 1952 Mulligan, who had moved to California, formed an innovative and successful piano-less quartet with trumpeter Chet Baker, drummer Chico Hamilton, and bassist Bob Whitlock. Mulligan would later form a decet based on the Birth of the Cool nonet.

In 1950, Stan Kenton disbanded his Innovations Orchestra in Los Angeles. Many of the musicians, some of whom had also played in Woody Herman's band, chose to remain in California. Trumpeter Shorty Rogers and drummers Stan Levey and Shelly Manne were central figures among this group of musicians. Much of this activity centered on the Hermosa Beach Lighthouse Café, where bassist Howard Rumsey led a house band, the Lighthouse All-Stars.

Manne suggested that these musicians' relaxed lifestyle in California was reflected in a laid-back, relaxed approach to jazz. Bob Rusch concurs:

The West coast sound perhaps didn't have the gravitas that the East coast had, but, after all, these were Californians enjoying the sun and the surf and the extent that celebrity offered itself through the studio work that the entertainment industry was offering. So I think, you know, you think of California as sun and surf, you think of New York City as cement and grit, and the music somewhat reflected that. One better than the other? Depends what you want.

During the 1950s, Chico Hamilton led an ensemble that (unusual for a jazz group) included a cellist, Fred Katz. Tanner, Gerow, and Megill liken Hamilton's music to chamber music, and have noted that Hamilton's "subtle rhythmic control and use of different drum pitches and timbres" were well-suited for this style of music.