John Barleycorn Must Die is the fourth studio album by English rock band Traffic, released in 1970. It marked the band's comeback after a brief disbandment, and peaked at number 5 on the Billboard 200, making it their highest-charting album in the US, and has been certified a gold record by the RIAA.

In late 1968, Traffic disbanded, with guitarist Dave Mason leaving the group for the second time prior to the completion of the Traffic album. In 1969, Steve Winwood joined the supergroup Blind Faith, while drummer and lyricist Jim Capaldi and woodwinds player Chris Wood turned to session work. Wood and Winwood also joined Blind Faith's drummer Ginger Baker in his post-Blind Faith group Ginger Baker's Air Force for their first album, Ginger Baker's Air Force (1970).

At the beginning of 1970, after the demise of Blind Faith, Winwood returned to the studio ostensibly to make his first solo album, originally to be titled Mad Shadows. He recorded two tracks with producer Guy Stevens, "Stranger to Himself" and "Every Mother's Son", but yearned for like-minded musicians to accompany, inviting Wood and Capaldi to join him. Thus Winwood's erstwhile solo album became the reunion of Traffic (minus Dave Mason), and a re-launch of the band's career. Mad Shadows would go on to be the title of Mott the Hoople's second album, also produced by Guy Stevens, and the new Winwood/Traffic album took its title from one of its tracks and became John Barleycorn Must Die.

The album featured influences from jazz and blues, but the version of the traditional English folk tune that provided the album's title, "John Barleycorn", also showed the musicians attending to a modern interpretation of traditional folk music in the vein of contemporary British bands Pentangle and Fairport Convention. Whereas previous Traffic albums had been dominated by more concise song structures, John Barleycorn saw the group develop into a looser, jam-oriented progressive rock and jazz fusion style, setting the tone for their subsequent output in the 1970s.

The album was reissued for compact disc in the UK on 1 November 1999, with five bonus tracks, including three recorded in concert from the Fillmore East in New York City. In the US, the remastered reissue of 27 February 2001 included only the two studio bonus tracks.

Steve Winwood oversaw a deluxe edition that was released on 15 March 2011, featuring the original studio album, digitally remastered on disc one, plus a second disc of bonus material, including more of the Fillmore East concert, with alternate mixes and versions of album tracks.

"John Barleycorn" is an English and Scottish folk song listed as number 164 in the Roud Folk Song Index. John Barleycorn, the song's protagonist, is a personification of barley and of the alcoholic beverages made from it: beer and whisky. In the song, he suffers indignities, attacks, and death that correspond to the various stages of barley cultivation, such as reaping and malting.

The song may have its origins in ancient English or Scottish folklore, with written evidence of the song dating it at least as far back as the Elizabethan era. The oldest versions are Scottish and include the Scots poem "Quhy Sowld Nocht Allane Honorit Be". In 1782, the Scottish poet Robert Burns published his own version of the song, which influenced subsequent versions.

The song survived into the twentieth century in the oral folk tradition, primarily in England, and many popular folk revival artists have recorded versions of the song. In most traditional versions, including the sixteenth century Scottish version entitled Alan-a-Maut, the plant's ill-treatment by humans and its re-emergence as beer to take its revenge are key themes.

In their notes to the Penguin Book of English Folk Songs (London, 1959), editors A. L. Lloyd and Ralph Vaughan Williams ponder whether the ballad is "an unusually coherent folklore survival" or "the creation of an antiquarian revivalist, which has passed into popular currency and become 'folklorised'". It has been theorised that the figure could have some relation to the semi-mythical wicker man ritual, which involves burning a man in effigy.

Kathleen Herbert draws a link between the mythical figure Beowa (a figure stemming from Anglo-Saxon paganism that appears in early Anglo-Saxon royal genealogies whose name means "barley") and the figure of John Barleycorn. Herbert says that Beowa and Barleycorn are one and the same, noting that the folksong details the suffering, death, and resurrection of Barleycorn, yet also celebrates the "reviving effects of drinking his blood".

The first song to personify Barley was called Allan-a-Maut ('Alan of the malt'), a Scottish song written prior to 1568; Allan is also the subject of "Quhy Sowld Nocht Allane Honorit Be", a fifteenth or sixteenth century Scots poem included in the Bannatyne Manuscript of 1568 and 17th century English broadsides.

Many field recordings of the song were made of traditional singers performing the song, mostly in England. In 1908, Percy Grainger used phonograph technology to record a Lincolnshire man named William Short singing the song; the recording can be heard on the British Library Sound Archive website.James Madison Carpenter recorded a fragment sung by a Harry Wiltshire of Wheald, Oxfordshire in the 1930s, which is available on the Vaughan Williams Memorial Library website as well as another version probably performed by a Charles Phelps of Avening, Gloucestershire. The Shropshire singer Fred Jordan was recorded singing a traditional version in the 1960s.

A version recorded in Doolin, Co. Clare, Ireland from a Michael Flanagan in the 1970s is available courtesy of the County Clare Library.

The Scottish singer Duncan Williamson also had a traditional version which was recorded.

Helen Hartness Flanders recorded a version sung by a man named Thomas Armstrong of Mooers Forks, New York, USA in 1935.

Many versions of the song have been recorded, including a popular version by the rock group Traffic, appearing on their 1970 album John Barleycorn Must Die. The song has also been recorded by Fire + Ice, Gae Bolg, Bert Jansch, the John Renbourn Group, Pentangle, Finest Kind, Martin Carthy, Roy Bailey, Martyn Bates in collaboration with Max Eastley, the Watersons, Steeleye Span, Joe Walsh, Steve Winwood with his band Traffic, Fairport Convention, Donnybrook Fair, Oysterband, Frank Black, Quadriga Consort, Maddy Prior, Heather Alexander, Leslie Fish, Tim van Eyken, Barry Dransfield, Of Cabbages and Kings, Winterfylleth (band), John Langstaff, Ayreheart, and many other performers. The song is also a central part of Simon Emmerson's The Imagined Village project. Martin and Eliza Carthy perform the song alongside Paul Weller on the Imagined Village album. Billy Bragg sang in Weller's place on live performances. Rock guitarist Joe Walsh performed the song live in 2007 as a tribute to Jim Capaldi. English folk musician Sam Lee recorded a version on his album "Old Wow," accompanied by a video filmed at Stonehenge.