"Blue Moon of Kentucky" is a waltz written in 1946 by bluegrass musician Bill Monroe and recorded by his band, The Blue Grass Boys. The song has since been recorded by many artists, including Elvis Presley. In 2003 the song was chosen to be added to the United States Library of Congress National Recording Registry.

"Blue Moon" is the official bluegrass song of Kentucky. In 2002, Monroe's version was one of 50 recordings chosen that year by the Library of Congress to be added to the National Recording Registry. In 2003, CMT ranked "Blue Moon" number 11 in its list of 100 Greatest Songs in Country Music.

Bill Monroe wrote the song in 1946, recording it for Columbia Records on September 16. It was released in early 1947. At the time, the Bluegrass Boys included vocalist and guitarist Lester Flatt and banjoist Earl Scruggs, who would later form their own bluegrass band, the Foggy Mountain Boys. Both Flatt and Scruggs performed on the recording, although Bill Monroe supplied the vocals on this song.

The song, described as a "bluegrass waltz", had become a United States wide hit by 1947 and also became enormously popular with other bluegrass, country and early rockabilly acts. The song was revered by the Grand Ole Opry and others;Carl Perkins played an uptempo version of this song in his early live performances.

The search for another song to release along with "That's All Right" at Sun Records in July 1954 led to "Blue Moon of Kentucky" via Bill Black. According to Scotty Moore:

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