It was ballet impresario Lincoln Kirstein who had the inspiration to bring together composer Aaron Copland and choreographer Eugene Loring to create a work based on the legend of Billy the Kid. Kirstein was particularly drawn to Walter Noble Burns' 1925 best-seller The Saga of Billy the Kid, a mix of lore, fantasy, and historical research. As related by Burns, Billy, a gambler, cattle rustler, and vigilante frontiersman, made his claim to fame in having killed a man for each of his 21 years. Loring devised a scenario which calls for four principals, along with "pioneers, men, women, Mexicans, and Indians." Much of the ballet's action, form, and mood reflects Burns' Saga, particularly the grotesque celebration which follows a central shoot-out scene.
Copland, having already composed works evocative of the American west and Mexico like El Salon Mexico (1933-36) and Saga of the Prairies (1937), was well prepared for this "cowboy ballet." The composer provided period flavor by incorporating six cowboy tunes into the score: "Great Granddad," "Git Along Little Dogie," "The Old Chisholm Trail," "Goodbye, Old Paint," "The Dying Cowboy," and "Trouble for the Range Cook."
Copland's score provides a vivid sonic depiction of prairie life. An opening processional is distinguished by Copland's trademark widely spaced "open" harmonies in the woodwinds, followed by a bass figure centered on a syncopated two-note motive. This plodding bass moves dramatically from pianissimo to a triple-forte climax, suggesting the laborious trudging of the settlers. The music of the processional brings the ballet full circle with its reappearance as the coda. "Street in a Frontier Town" moves from pastoral innocence to mechanistic violence, incorporating several cowboy tunes along the way. The rest of Billy's story moves unfolds in short vignettes, including "Card Game at Night" (also known as "Prairie Night"), which draws upon the familiar image of the lone cowboy, including snatches of "The Dying Cowboy." "Gun Battle" is dominated by violent percussion, the sounds of gunfire represented by snare and bass drums. In "Celebration After Billy's Capture" Copland neatly transforms the trudging bass of the opening processional into a dissonant "oompah" figure that underpins a crude bitonal melody, while a waltz section transforms "Trouble for the Range Cook" into an ironic ditty with solos in the trombone and bassoon. "Billy's Death" is a solemn epilogue for strings, harp, and winds.
Billy the Kid was first performed by the Ballet Caravan in Chicago in a two-piano version on October 6, 1938. The familiar version for full orchestra was premiered in New York on May 24, 1939 to critical and popular raves. In 1940 Copland extracted a concert suite from the ballet, the form in which the music is today most frequently heard.