Durham Castle is a Norman castle in the city of Durham, England, which has been occupied since 1837 by University College, Durham after its previous role as the residence of the Bishops of Durham. Designated since 1986 as a cultural World Heritage Site in England, along with Durham Cathedral, the castle is open to the general public to visit, but only through guided tours, since it is in use as a working building and is home to over 100 students. The castle stands on top of a hill above the River Wear on Durham's peninsula, opposite Durham Cathedral (grid reference NZ274423).

Construction of the castle, of the motte and bailey design favoured by the Normans, began in 1072 under the orders of William the Conqueror, six years after the Norman conquest of England, and soon after the Normans first came to the North. The construction took place under the supervision of Waltheof, Earl of Northumbria, until he rebelled against William and was executed in 1076. Stone for the new buildings was cut from the cliffs below the walls and moved up using winches.

The holder of the office of the bishop of Durham, Bishop Walcher at the time, was appointed by the king to exercise royal authority on his behalf, with the castle being his seat. Adding to his status by the purchase of the Earldom of Northumbria, Walcher began a line of prince-bishops which continued until the Bishops of Durham lost their temporal powers under the Durham (County Palatine) Act 1836. The prince-bishops were entitled to raise an army, levy taxes and mint their own coinage. The wide remit granted them by the English crown allowed them virtual autonomy to act as a defence both against Scottish incursions from the north, and internal rebellions.

Walcher continued the building of the castle, as a combination of bishops' palace and defensive stronghold. Inner and outer baileys and a keep were constructed. The earliest structures may have been of wood, but there is evidence of building in stone from the end of the 11th century. In May 1080, the castle was attacked and besieged for four days by rebels from Northumbria and Bishop Walcher was killed.

In the 12th century, Bishop Pudsey (Hugh de Puiset) built the Norman archway and the Galilee of the cathedral. In 1177, King Henry II of England seized the castle after a disagreement with de Puiset. Other major alterations were made by Bishop Thomas Hatfield in the 1300s, including a rebuilding of the keep and enlargement of the keep mount.

The castle has a large Great Hall, originally called a Dining Hall, created by Bishop Antony Bek in the early 14th century; Bishop Hatfield added a wooden minstrels' gallery. The hall was modified and enlarged, then reduced, in size by subsequent bishops. Today, the Hall is 14 metres (46 ft) high and over 30 metres (98 ft) long.

The Castle remained the bishop's palace for the Bishop of Durham until Auckland Castle was made the bishops' residence in 1832; the current bishop still maintains offices at that castle, roughly ten miles to the south. Subsequently, Durham castle was donated to the University of Durham by Bishop William Van Mildert and would later become the college. The college did not occupy the castle until 1837, after the next Bishop, Edward Maltby, had completed renovations of the building.

The cathedral was targeted for a Baedeker Blitz or bombing raid by Germany but escaped because fog rolled in and blocked the pilots' view.