Origins

According to biographers of McCartney and The Beatles, McCartney composed the entire melody in a dream one night in his room at the Wimpole Street home of his then girlfriend Jane Asher and her family. Upon waking, he hurried to a piano, turned on a tape recorder, and played the tune to avoid letting it slip into the recesses of his mind.

McCartney's initial concern was that he had subconsciously plagiarised someone else's work (known as cryptomnesia). As he put it, "For about a month I went round to people in the music business and asked them whether they had ever heard it before."Eventually it became like handing something in to the police. I thought if no-one claimed it after a few weeks then I could have it".

Upon being convinced that he had not robbed anybody of his melody, McCartney began writing lyrics to suit it. As Lennon and McCartney were known to do at the time, a substitute working lyric, entitled "Scrambled Eggs", was used for the song until something more suitable was written. In his biography, "Many Years From Now", McCartney recalled: "So first of all I checked this melody out, and people said to me, 'No, it's lovely, and I'm sure it's all yours.' It took me a little while to allow myself to claim it, but then like a prospector I finally staked my claim; stuck a little sign on it and said, 'Okay, it's mine!' It had no words. I used to call it 'Scrambled Eggs'."

During the shooting of Help!, a piano was placed on one of the stages where filming was being conducted. McCartney would take advantage of this opportunity to perform "Scrambled Eggs" accompanied by the piano. Richard Lester, the director, was greatly annoyed by this, and eventually lost his temper, telling McCartney to finish writing the song, or he would have the piano removed. McCartney's original lyrics were, "Scrambled eggs, Oh, baby how I love your legs."

McCartney originally claimed he had written "Yesterday" during The Beatles' tour of France in 1964; however, the song was not released until the summer of 1965. During the intervening time, The Beatles released two albums, Beatles for Sale and A Hard Day's Night, both of which could have included "Yesterday". Although McCartney has never elaborated his claims, it is likely that the reason for such a long delay, if it existed, was a disagreement between McCartney and George Martin regarding the song's arrangement, or, equally likely, the distaste of the other Beatles for the song.

Lennon later indicated that the song had been around for a while before:

"The song was around for months and months before we finally completed it. Every time we got together to write songs for a recording session, this one would come up. We almost had it finished. Paul wrote nearly all of it, but we just couldn't find the right title. We called it 'Scrambled Eggs' and it became a joke between us. We made up our minds that only a one-word title would suit, we just couldn't find the right one. Then one morning Paul woke up and the song and the title were both there, completed. I was sorry in a way, we'd had so many laughs about it."

McCartney said the breakthrough with the lyrics came during a trip to Portugal in May 1965:

"I remember mulling over the tune 'Yesterday', and suddenly getting these little one-word openings to the verse. I started to develop the idea ... da-da da, yes-ter-day, sud-den-ly, fun-il-ly, mer-il-ly and Yes-ter-day, that's good. All my troubles seemed so far away. It's easy to rhyme those a's: say, nay, today, away, play, stay, there's a lot of rhymes and those fall in quite easily, so I gradually pieced it together from that journey. Sud-den-ly, and 'b' again, another easy rhyme: e, me, tree, flea, we, and I had the basis of it."

On 27 May 1965, McCartney and Asher flew to Lisbon for a holiday in the Algarve, and he borrowed an acoustic guitar from Bruce Welch—whose house they were staying in—and completed the work on "Yesterday".

The song was offered as a demo to Chris Farlowe prior to The Beatles recording it, but he turned it down as he considered it "too soft."