Derwent Valley Mills is a World Heritage Site along the River Derwent in Derbyshire, England, designated in December 2001. It is administered by the Derwent Valley Mills Partnership. The modern factory, or 'mill', system was born here in the 18th century to accommodate the new technology for spinning cotton developed by Richard Arkwright. With advancements in technology, it became possible to produce cotton continuously. The system was adopted throughout the valley, and later spread so that by 1788 there were over 200 Arkwright-type mills in Britain. Arkwright's inventions and system of organising labour was exported to Europe and the United States.
Water-power was first introduced to England by John Lombe at his silk mill in Derby in 1719, but it was Richard Arkwright who applied water-power to the process of producing cotton in the 1770s. His patent of a water frame allowed cotton to be spun continuously, meaning it could be produced by unskilled workers. Cromford Mill was the site of Arkwright's first mill, with nearby Cromford village significantly expanded for his then-new workforce; this system of production and workers' housing was copied throughout the valley. To ensure the presence of a labour force, it was necessary to construct housing for the mill workers. Thus, new settlements were established by mill owners around the mills – sometimes developing a pre-existing community – with their own amenities such as schools, chapels, and markets. Most of the housing still exists and is still in use. Along with the transport infrastructure form part of the site. A transport infrastructure was built to open new markets for the mills' produce.
Mills and workers' settlements were established at Belper, Darley Abbey, and Milford by Arkwright's competitors. Arkwright-type mills were so successful that sometimes they were copied without paying royalties to Richard Arkwright. The cotton industry in the Derwent Valley went into decline in the first quarter of the 19th century as the market shifted towards Lancashire which was better position in relation to markets and raw materials. The mills and their associated buildings are well preserved and have been reused since the cotton industry declined. Many of the buildings within the World Heritage Site are also listed buildings and Scheduled Monuments. Some of the mills now contain museums and are open to the public.