Lennon–McCartney was the songwriting partnership between the English musicians John Lennon (1940–1980) and Paul McCartney (born 1942) of the Beatles. It is widely considered one of the greatest, best known, and most successful musical collaborations ever by records sold, with the Beatles selling more than 600 million records worldwide as of 2004^[update]. Between 5 October 1962 and 8 May 1970, the partnership published approximately 180 jointly credited songs, of which the vast majority were recorded by the Beatles, forming the bulk of their catalogue.

Unlike many songwriting partnerships that comprise a separate composer and lyricist, such as George and Ira Gershwin, Richard Rodgers and Oscar Hammerstein II, John Kander and Fred Ebb, or Elton John and Bernie Taupin, both Lennon and McCartney wrote music and lyrics. Sometimes, especially early on, they would collaborate extensively when writing songs, working "eyeball to eyeball" as Lennon phrased it. During the latter half of their partnership, it became more common for either of them to write most of a song on their own with minimal input from the other, and sometimes none at all. By an agreement made before the Beatles became famous, Lennon and McCartney were credited equally with songs that either one of them wrote while their partnership lasted.

Lennon–McCartney compositions have been the subject of numerous cover versions. According to Guinness World Records, "Yesterday" has been recorded by more musicians than any other song.

Lennon and McCartney separately experimented with songwriting before having met each other. McCartney wrote his first song fragments—including "I Call It Suicide" and the tune of what eventually became "When I'm Sixty-Four"—in spring 1956, just shy of 14 years old. Lennon's first song, "Calypso Rock", was written about March 1957.

Although McCartney had previously seen and noticed Lennon in the local area without knowing who he was, the pair first met on 6 July 1957, at a local church fête, where 16-year-old Lennon was playing with his skiffle group, the Quarrymen. The 15-year-old McCartney, brought along by a mutual friend, Ivan Vaughan, impressed Lennon with his ability on the guitar and his version of Eddie Cochran's "Twenty Flight Rock". Soon afterwards, Lennon asked McCartney if he would join the Quarrymen; McCartney accepted. The duo's first musical idols were the Everly Brothers, Little Richard, Chuck Berry, Elvis Presley, Buddy Holly, and Smokey Robinson and the Miracles, and they learned many of their songs and imitated their sound. Their first compositions were written at McCartney's home (20 Forthlin Road), at Lennon's aunt Mimi's house (251 Menlove Avenue), or at the Liverpool Institute.

The first song that Lennon and McCartney wrote together, according to Mark Lewisohn, was titled "Too Bad About Sorrows" (January 1958), followed soon after by "Just Fun". The two boys kept song scraps in a notebook, the top of each page noting "another Lennon–McCartney original." This formulation was inspired by theatrical writing teams like Rodgers and Hammerstein. They often invited friends—including George Harrison, Nigel Walley, Barbara Baker, and Lennon's art school colleagues—to listen to performances of their new songs. However, they did not perform these songs with the Quarrymen. The pair continued to write throughout 1958 and 1959, though by summer 1959 they were writing mostly separately and presenting each other with their own songs for approval. Most compositions during this time were by McCartney. Early versions of numerous songs the Beatles and other artists recorded emerged at this time, including "Love Me Do", "I'll Follow the Sun", "Love of the Loved", "A World Without Love", and "What Goes On".

In May 1960, Lennon's art college classmate Stuart Sutcliffe joined the group, soon known as the Beatles. Sutcliffe's close friendship with Lennon and new role in the band made McCartney envious and disrupted the Lennon–McCartney songwriting dynamic. The pair wrote no new songs in 1960, despite needing to fill hours of stage time in their Hamburg residency. Lewisohn observed, "as a bar band, it was important the Beatles played songs people knew or might know." The dry spell continued on the next year, as neither Lennon nor McCartney wrote any new songs in 1961. The pair kept their songwriting a secret from associates and fans alike; on the rare occasions they played one of their own songs, they would not announce them as such to the audience. Possibly the only instance of such a performance was a rendition of "One After 909" at the Top Ten Club at Astrid Kirchherr's request. It was not until late 1961, around the time the Beatles met Brian Epstein, that they began regularly performing some of their original songs.

The Lennon–McCartney songwriting partnership re-emerged forcefully in 1962. Among the songs the Beatles recorded at their failed 1 January 1962 Decca Records audition were three old originals—"Like Dreamers Do", "Love of the Loved", and "Hello Little Girl". Soon after, a tape of this performance of "Like Dreamers Do" was played for EMI song publishers Ardmore & Beechwood, who lobbied EMI management to sign the Beatles as recording artists so Ardmore & Beechwood could obtain exclusive publishing rights to Lennon–McCartney songs. Around March 1962, John and Paul each wrote their first songs since 1959—"Ask Me Why" and "Pinwheel Twist", respectively. In May, Paul wrote "P.S. I Love You".