"Hey Jude" is a song by the English rock band the Beatles that was released as a non-album single in August 1968. It was written by Paul McCartney and credited to the Lennon–McCartney partnership. The single was the Beatles' first release on their Apple record label and one of the "First Four" singles by Apple's roster of artists, marking the label's public launch. "Hey Jude" was a number-one hit in many countries around the world and became the year's top-selling single in the UK, the US, Australia and Canada. Its nine-week run at number one on the Billboard Hot 100 tied the all-time record in 1968 for the longest run at the top of the US charts, a record it held for nine years. It has sold approximately eight million copies and is frequently included on music critics' lists of the greatest songs of all time.

The writing and recording of "Hey Jude" coincided with a period of upheaval in The Beatles. The ballad evolved from "Hey Jules", a song McCartney wrote to comfort John Lennon's young son Julian Lennon, after Lennon had left his wife Cynthia Lennon for the Japanese artist Yoko Ono. The lyrics espouse a positive outlook on a sad situation, while also encouraging "Jude" to pursue his opportunities to find love. After the fourth verse, the song shifts to a coda featuring a "Na-na-na na" refrain that lasts for over four minutes.

"Hey Jude" was the first Beatles song to be recorded on eight-track recording equipment. The sessions took place at Trident Studios in central London, midway through the recording of the group's self-titled double album (also known as the White Album), and led to an argument between McCartney and George Harrison over the song's guitar part. Ringo Starr later left the band only to return shortly before they filmed the promotional clip for the single. The clip was directed by Michael Lindsay-Hogg and first aired on David Frost's UK television show Frost on Sunday. Contrasting with the problems afflicting the band, this performance captured the song's theme of optimism and togetherness by featuring the studio audience joining the Beatles as they sang the coda.

At over seven minutes in length, "Hey Jude" was the longest single to top the British charts up to the time. Its arrangement and extended coda encouraged many imitative works through to the early 1970s. In 2013, Billboard magazine named it the 10th "biggest" song of all time in terms of chart success. McCartney has continued to perform "Hey Jude" in concert since Lennon's murder in 1980, leading audiences in singing the coda. Julian Lennon and McCartney have each purchased memorabilia related to the song's creation.

I started with the idea "Hey Jules," which was Julian, don't make it bad, take a sad song and make it better. Hey, try and deal with this terrible thing. I knew it was not going to be easy for him. I always feel sorry for kids in divorces ...

In May 1968, John Lennon and his wife Cynthia Lennon separated due to his affair with artist Yoko Ono. The following month, Paul McCartney drove out to visit the Lennons' five-year-old son Julian Lennon, at Kenwood, the family's home in Weybridge. Cynthia had been part of the Beatles' social circle since before the band's rise to fame in 1963; McCartney later said he found it "a bit much for them suddenly to be personae non gratae and out of my life". Cynthia Lennon recalled of McCartney's surprise visit: "I was touched by his obvious concern for our welfare ... On the journey down he composed 'Hey Jude' in the car. I will never forget Paul's gesture of care and concern in coming to see us." The song's original title was "Hey Jules", and it was intended to comfort Julian from the stress of his parents' separation. McCartney said, "I knew it was not going to be easy for him", and that he changed the name from "Jules" to "Jude" "because I thought that sounded a bit better".

According to music journalist Chris Hunt, in the weeks after writing the song, McCartney "test[ed] his latest composition on anyone too polite to refuse. And that meant everyone." On 30 June, after recording the Black Dyke Mills Band's rendition of his instrumental "Thingumybob" in Yorkshire, McCartney stopped at the village of Harrold in Bedfordshire and performed "Hey Jude" at a local pub. He also regaled members of the Bonzo Dog Band with the song while producing their single "I'm the Urban Spaceman", in London, and interrupted a recording session by the Barron Knights to do the same. Ron Griffiths of the group the Iveys – soon to be known as Badfinger and, like the Black Dyke Mills Band, an early signing to the Beatles' new record label Apple Records – recalled that on one of their first days in the studio, McCartney "gave us a full concert rendition of 'Hey Jude'".

If you think about it ... Yoko's just come into the picture. He's saying. "Hey, Jude – Hey, John." I know I'm sounding like one of those fans who reads things into it, but you can hear it as a song to me. The words "Go out and get her" – subconsciously he was saying, Go ahead, leave me. On a conscious level, he didn't want me to go ahead.