Most of the 20th century's great vocalists performed in the jazz idiom, though not all rank in the style known as vocal jazz. While singers from Russ Columbo to Doris Day to Johnny Mathis relied on talent and vocal strength alone to carry material, vocal jazz artists instead chose to interpret standards in much the same way as the great jazz instrumentalists, so their readings of the great American songbook required talents related to improvisation, musicianship, harmony, even personalization to bring new meanings to the lyrics. A pair of early giants, Louis Armstrong and Bing Crosby, recorded distinctive readings of standards, relying on a delivery that was casual yet very focused -- an almost total break with the professional vocal traditions of the past. From the big-band era came dozens of major jazz vocalists, and in fact, most of the best: Frank Sinatra, Billie Holiday, Ella Fitzgerald, Mel Tormé, Anita O'Day, Sarah Vaughan, Peggy Lee, Joe Williams; all of them worked long hours touring with swing bands, and most were repaid in kind with major success during the post-war era, when the style really bloomed.
Though it wasn't always easy separating jazz vocalists from traditional pop singers, many in the jazz repertoire usually earned the tag by delivering variations of their material in performance or scatting in emulation of a jazz soloist. They also generally refused no-name orchestras and generic pop hits of the day, preferring instead the work of talented arrangers (Nelson Riddle, Billy May) and truly great composers (Irving Berlin, Cole Porter, the Gershwins). Singers of the post-war era began stretching the concepts of not swing but bop, interpreting the frantic tempoes and exploratory solos of jazz instrumentalists with their own vocal experiments. Lambert, Hendricks & Ross indulged in manic harmonies, while a host of singers (including Betty Carter, Mark Murphy, and Abbey Lincoln) explored different charts, radical material, and much improvisation. Even while the ranks of jazz vocalists thinned during the 1970s and '80s, many artists continued in the style.