A childlike singalong written in the music hall tradition, “All Together Now” was written in the studio for the Yellow Submarine film.

Paul McCartney came up with the idea for the song and wrote the verses and chorus, while Lennon contributed the ‘Sail the ship, chop the tree’ middle section.

“All Together Now” features during an animated sequence in Yellow Submarine, and again towards the end of the film, introduced by the Beatles themselves.

It’s really a children’s song. I had a few young relatives and I would sing songs for them. I used to do a song for kids called ‘Jumping Round The Room,’ very similar to ‘All Together Now,’ and then it would be ‘lying on your backs’, all the kids would have to lie down, then it would be ‘skipping round the room’, ‘jumping in the air’. It’s a play away command song for children. It would be in G, very very simple chords, only a couple of chords, so that’s what this is. There’s a little subcurrent to it but it’s just a singalong really. A bit of a throwaway.
-Paul McCartney via Beatles Ebooks

McCartney was delighted when the song became a popular terrace chant at football matches shortly after its release in early 1969.

Jazz musician Paul Horn remembers him singing it in India; instead of ‘H, I, J, I love you’, he is said to have sung ‘E, F, G, H, I, jai Guru Dev’ in honour of Maharishi’s spiritual master.

I put a few lines in it somewhere, probably.
-John Lennon via Beatles Ebooks

The Beatles completed the song in a six-hour session on 12 May 1967. In the absence of George Martin, the song was essentially produced by McCartney with assistance from engineer Geoff Emerick.

It took the group nine takes to get right. They then added a number of overdubs, including ukulele and harmonica, both played by John Lennon.