In vocal jazz, scat singing is vocal improvisation with wordless vocables, nonsense syllables or without words at all. Scat singing gives singers the ability to sing improvised melodies and rhythms, to create the equivalent of an instrumental solo using their voice.

Though scat singing is improvised, the melodic lines are often variations on scale and arpeggio fragments, stock patterns and riffs, as is the case with instrumental improvisers as well as singers. As well, scatting usually incorporates musical structure. All of Ella Fitzgerald's scat performances of "How High the Moon", for instance, use the same tempo, begin with a chorus of a straight reading of the lyric, move to a "specialty chorus" introducing the scat chorus, and then the scat itself.Will Friedwald has compared Ella Fitzgerald to Chuck Jones directing his Roadrunner cartoon—each uses predetermined formulas in innovative ways. Among the greatest exponents of the scat style was Mel Tormé, a child prodigy drummer who went on to become one of the most influential jazz performers of the 20th century. Tormé's effortless scatting was built on his outstanding big-band arrangement and multi-instrumentalist skills.

Judy Niemack (b. March 11, 1954, Pasadena, California) is an American jazz vocalist.

Niemack sang in a church choir from age seven. She decided on a professional career in singing at age 17, and soon after met Warne Marsh, who encouraged her to explore jazz. She studied jazz at Pasadena City College, and later at the New England Conservatory of Music and the Cleveland Institute of Music. Her debut album was released in 1977; she has recorded several albums under her own name in addition to working with Toots Thielemans, James Moody, Lee Konitz, Clark Terry, Kenny Barron, Fred Hersch, Kenny Werner, Joe Lovano, Eddie Gomez, and the Widespread Depression Jazz Orchestra. She has toured Europe many times and also teaches music.

Cabell "Cab" Calloway III (December 25, 1907 – November 18, 1994) was an American jazz singer and bandleader. He was strongly associated with the Cotton Club in Harlem, New York City where he was a regular performer.

Calloway was a master of energetic scat singing and led one of the United States' most popular African American big bands from the start of the 1930s through the late 1940s. Calloway's band featured performers including trumpeters Dizzy Gillespie and Adolphus "Doc" Cheatham, saxophonists Ben Webster and Leon "Chu" Berry, New Orleans guitar ace Danny Barker, and bassist Milt Hinton. Calloway continued to perform until his death in 1994 at the age of 86.

Cab Calloway was born in a middle-class family in Rochester, New York, on Christmas Day in 1907. He lived there until moving to Baltimore, Maryland in 1918. His father, Cabell Calloway II, was a lawyer and his mother, Martha Eulalia Reed, was a teacher and church organist. When Cab was young, he enjoyed singing in church. His parents recognized their son's musical talent and he began private voice lessons in 1922. He continued to study music and voice throughout his formal schooling. Despite his parents' and vocal teachers' disapproval of jazz, Calloway began frequenting and eventually performing in many of Baltimore's jazz clubs, where he was mentored by drummer Chick Webb and pianist Johnny Jones.