The River Dee (Welsh: Afon Dyfrdwy, Latin: Deva Fluvius) is a 70-mile (110 km) long river in the United Kingdom. It travels through Wales and England and also forms part of the border between the two countries.

The river rises in Snowdonia, Wales, flows east via Chester, England, and discharges to the sea into an estuary between Wales and the Wirral Peninsula in England.

The total catchment area of the River Dee up to Chester Weir is 1,816.8 square kilometres (701.5 sq mi). The average rainfall over the catchment is estimated to be 640 millimetres (25 in) yielding an average flow of 37 m³/s. The larger reservoirs in the catchment are:

The River Dee has its source on the slopes of Dduallt above Llanuwchllyn in the mountains of Snowdonia in Merioneth, Gwynedd, Wales, and then passes through Bala Lake. The path of the river trends generally east-south-east as it descends off the Ordovician Denbigh Moors, over the man-made Horseshoe Falls and through Llangollen, generally skirting the outcropping Karstic limestone exposures north of Llangollen. East of Llangollen, Thomas Telford's Pontcysyllte Aqueduct, of 1805, carries the Shropshire Union Canal 120-foot (37 m) overhead.

Wales ⁱ/ˈweɪlz/ (Welsh: Cymru;Welsh pronunciation: [ˈkəm.rɨ] ( listen)) is a country that is part of the United Kingdom and the island of Great Britain,bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km² (8,023 sq mi). Wales has over 1,200 km (750 mi) of coastline, including its offshore islands; the largest, Anglesey (Ynys Môn), is also the largest island in the Irish Sea. Wales is largely mountainous, with its highest peaks in the north and central areas, especially in Snowdonia (Eryri), which contains Snowdon (Yr Wyddfa), its highest summit.

During the Iron Age and early medieval period, Wales was inhabited by the Celtic Britons. A distinct Welsh national identity emerged in the centuries after the Roman withdrawal from Britain in the 5th century, and Wales is regarded as one of the modern Celtic nations today. Gruffydd ap Llywelyn was recognised as King of Wales in 1057. Llywelyn ap Gruffydd's death in 1282 marked the completion of Edward I of England's conquest of Wales. The castles and town walls erected to ensure its permanence are now UNESCO World Heritage Sites. Owain Glyndŵr briefly restored independence to what was to become modern Wales, in the early 15th century. Wales was subsequently annexed by England under the Laws in Wales Acts 1535–1542 since when, excluding those matters now devolved to Wales, English law has been the legal system of Wales and England. Distinctive Welsh politics developed in the 19th century. Welsh Liberalism, exemplified in the early 20th century by Lloyd George, was displaced by the growth of socialism and the Labour Party. Welsh national feeling grew over the century; Plaid Cymru was formed in 1925 and The Welsh Language Society in 1962. The National Assembly for Wales, created in 1999 following a referendum, holds responsibility for a range of devolved policy matters.

River Dee may refer to: