"Lucy in the Sky with Diamonds" is a song written primarily by John Lennon and credited to Lennon–McCartney, for the Beatles' 1967 album Sgt. Pepper's Lonely Hearts Club Band. Lennon's son Julian inspired the song with a nursery school drawing he called "Lucy—in the sky with diamonds". Shortly after the song's release, speculation arose that the first letter of each of the title nouns intentionally spelled "LSD". Lennon consistently denied this, insisting the song was inspired by Lewis Carroll's Alice in Wonderland books, a claim repeatedly confirmed by Paul McCartney.

Despite persistent rumours, the song was never officially banned by the BBC, and aired contemporaneously on BBC Radio at least once, on 20 May 1967.

Most of the song is in simple triple metre (3
4 time), but the chorus is in 4
4 time. The song modulates between musical keys, using the key of A major for verses, B♭ major for the pre-chorus, and G major for the chorus. It is sung by Lennon over an increasingly complicated underlying arrangement which features a tamboura, played by George Harrison, lead electric guitar put through a Leslie speaker, played by Harrison, and a counter melody on Lowrey organ played by McCartney and taped with a special organ stop sounding "not unlike a celeste". Session tapes from the initial 1 March 1967 recording of this song reveal Lennon originally sang the line "Cellophane flowers of yellow and green" as a broken phrase, but McCartney suggested that he sing it more fluidly to improve the song.

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