All four Beatles are credited with writing this song. It was the first song where composer credits were shared by the whole group.
This was the first instrumental song by The Beatles to be published by EMI. It was also the only Beatles instrumental released on Parlophone Records, their British label. They had recorded an instrumental for Rubber Soul called "12-Bar Original" in 1965, which went un-released.
The Beatles used this in their movie Magical Mystery Tour.
This is one of the few Beatles songs featuring the Mellotron, which was played by John Lennon. Others are " Strawberry Fields Forever" and "I am the Walrus." (thanks, Mike - Mountlake Terrace, Washington, for all above)
The original title was "Aerial Tour Instrumental." (thanks, Morgan - Fargo, ND)