Who wrote the song "Yesterday"?

Paul McCartney wrote the song "Yesterday" for the Beatles.

The melody reportedly came to McCartney in a dream while he was staying at Jane Asher’s family home in London. Worried that he might have unconsciously copied another song, he played it for people in the music business before deciding it was original. The tune temporarily carried the humorous working lyric "Scrambled Eggs" until McCartney and John Lennon developed the final words.

Although the song is officially credited to Lennon–McCartney, McCartney wrote the music and lyrics. It was recorded in June 1965 and released on the Beatles’ album Help! later that year. McCartney’s lead vocal and acoustic guitar, accompanied by a string quartet, made it essentially the Beatles’ first recording to feature one member without the other Beatles playing instruments.

A common mix-up is confusing songwriting credit with performance credit: the Beatles performed the song, but McCartney was its principal writer.