This was the last song mixed for Abbey Road, and it was the last time all four Beatles were in the studio together. It was the result of 2 unfinished songs woven together. Before they broke up, The Beatles had a lot of partially completed songs, many of which ended up in their solo work.
John Lennon wrote this about Yoko. Lennon was experimenting in heavy rock, so the song has few lyrics and long stretches of repeated chords. (thanks, Bertrand - Paris, France)
The rhythm was based on Mel Torme's "Coming Home Baby."
With the exception of " Revolution 9," this was The Beatles longest song.
John Lennon sang this monofonic, as some of the troubadours sang in the Middle Ages: There is no chord behind the melody, but an instrument follows the singer's melody. The song ends with an orchestra arrangement, which was Lennon's idea, and is very much similar to the end of "Entry of the Gods into Valhalla" in "Das Rheingold" by Richard Wagner. (thanks to Johan Cavalli, who is a music historian in Stockholm)
George Harrison played a Moog Synthesizer on this track. It is one of the first uses of the instrument, which was custom-made for Harrison.
The guitars were overdubbed many times to get a layered sound.
This song contains an accidental background lyric. On stereo, play the song at 4:30 and listen very closely to the left speaker. In the bass break after John's scream, you can faintly hear someone say, "What was that about!?" presumably in response to the scream. (thanks, Tommy - Alameda, CA)