Halifax is a town in the Metropolitan Borough of Calderdale, in West Yorkshire, England. It is in the eastern foothills of the Pennines. In the 15th century, the town became an economic hub of the old West Riding of Yorkshire, primarily in woollen manufacture with the large Piece Hall square later built for trading wool in the town centre. The town was a thriving mill town during the Industrial Revolution with the Dean Clough Mill buildings a surviving landmark. In the 2021 census, the town was recorded as having a population of 88,134.^{[citation needed]} It is also the administrative centre of the Calderdale Metropolitan Borough.

The town's name was recorded in about 1091 as Halyfax, most likely from the Old English halh-gefeaxe, meaning "area of coarse grass in the nook of land". This explanation is generally preferred to derivations from the Old English halig (holy), in hālig feax or "holy hair", proposed by 16th-century antiquarians. The probably-incorrect interpretation gave rise to two legends. One concerned a maiden killed by a lustful priest whose advances she spurned; another held that the head of Saint John the Baptist was buried here after his execution.

The legend is almost certainly medieval rather than ancient, although the town's coat of arms carries an image of the saint. Another explanation is a corruption of the Old English hay and ley, as a clearing or meadow. This etymology is based on Haley Hill, the nearby hamlet of Healey (another corruption), and the common occurrence of the surnames Hayley and Haley around Halifax. The derivation from halig has given rise to the demonym Haligonian, which is of recent origin and not in universal use.

The Earldom of Halifax took the name of the town. Its first creation, in the Peerage of England in 1677, was for George Savile, who was created Baron Savile of Eland and Viscount Halifax in 1668 and later became the Marquess of Halifax (this creation of the earldom became extinct in 1700). George Montagu-Dunk, 2nd Earl of Halifax, (2nd order of the 3rd creation) became the President of the Board of Trade in 1748. In 1749 the city of Halifax, the capital of Nova Scotia, Canada, was named in his honour. The Halifax River in Central Florida, United States, was also named after him.

Halifax is not mentioned in the Domesday Book, and evidence of the early settlement is unclear. By the 12th century the township had become the religious centre of the vast parish of Halifax, which extended from Brighouse in the east to Heptonstall in the west. Halifax Minster, parts of which date from the 12th century is dedicated to St John the Baptist. The minster's first organist, in 1766, was William Herschel, who discovered the planet Uranus. The coat of arms of Halifax include the chequers from the original coat of arms of the Earls Warenne, who held the town during Norman times.

Halifax was notorious for its gibbet, an early form of guillotine used to execute criminals by decapitation, that was last used in 1650. A replica has been erected on the original site in Gibbet Street. Its original blade is on display at Bankfield Museum. Punishment in Halifax was notoriously harsh, as remembered in the Beggar's Litany by poet John Taylor (1580–1654), a prayer whose text included "From Hull, from Halifax, from Hell, 'tis thus, From all these three, Good Lord deliver us.".

The town's 19th-century wealth came from the cotton, wool and carpet industries and like most other Yorkshire towns, it had a large number of weaving mills many of which have been lost or converted to alternative use.

In November 1938, in an incident of mass hysteria, many residents believed a serial killer, the Halifax Slasher, was on the loose. Scotland Yard concluded there were no attacks after several locals admitted they had inflicted wounds on themselves.