Dewsbury is a market town in the Metropolitan Borough of Kirklees in West Yorkshire, England. It lies on the River Calder and on an arm of the Calder and Hebble Navigation waterway. It is to the west of Wakefield, east of Huddersfield and south of Leeds. Historically a part of the West Riding of Yorkshire, after undergoing a period of major growth in the 19th century as a mill town, Dewsbury went through a period of decline. Dewsbury forms part of the Heavy Woollen District of which it is the largest town. The population of the built-up area was 63,722 at the 2021 Census.

The Domesday Book of 1086 records the name as Deusberie, Deusberia, Deusbereia, or Deubire, literally "Dewi's fort", Dewi being an old Welsh name (equivalent to David) and "bury" coming from the old English word "burh", meaning fort.

Other, less supported, theories exist as to the name's origin. For example, that it means "dew hill", from Old English dēaw (genitive dēawes), "dew", and beorg, "hill" (because Dewsbury is built on a hill). It has been suggested that dēaw refers to the town's proximity to the water of the River Calder.

In the past other origins were proposed, such as "God's fort", from Welsh Duw, "God". "Antiquarians supposed the name, Dewsbury, to be derived from the original planter of the village, Dui or Dew, who … had fixed his abode and fortified his "Bury". Another conjecture holds, that the original name is Dewsborough, or God's Town" (1837)

In Anglo-Saxon times, Dewsbury was a centre of considerable importance. The ecclesiastical parish of Dewsbury encompassed Huddersfield, Mirfield and Bradford. Ancient legend records that in 627 Paulinus, the Bishop of York, preached here on the banks of the River Calder. Numerous Anglian graves have been found in Dewsbury and Thornhill.

Dewsbury Minster lies near the River Calder, traditionally on the site where Paulinus preached. Some of the visible stonework in the nave is Saxon, and parts of the church also date to the 13th century. The tower houses "Black Tom", a bell which is rung each Christmas Eve, one toll for each year since Christ's birth, known as the "Devil's Knell", a tradition dating from the 15th century. The bell was given by Sir Thomas de Soothill, in penance for murdering a servant boy in a fit of rage. The tradition was commemorated on a Royal Mail postage stamp in 1986.

In the Domesday Book of 1086, Dewsbury was in Morley wapentake, but with a recorded population of only nine households it was a relatively small settlement at that time. The Agbrigg and Morley wapentakes were administratively combined into the Agbrigg and Morley wapentake in the 13th century. When they were separated for administrative purposes in the mid-19th century, Dewsbury parish had grown to straddle the border between both wapentakes, hence being mainly in the Lower Division of the Wapentake of Agbrigg.

Dewsbury market was established in the 14th century for local clothiers. Occurrences of the plague in 1593 and 1603 closed the market and it reopened in 1741.