The Palace of Westminster, also known as the Houses of Parliament, is the seat of the two houses of the Parliament of the United Kingdom—the House of Lords and the House of Commons. The Palace lies on the north bank of the River Thames in the London borough of the City of Westminster, close to the government buildings of Whitehall.

The palace contains around 1,100 rooms, 100 staircases and 5 kilometres (3 mi) of corridors. Although the building mainly dates from the 19th century, remaining elements of the original historic buildings include Westminster Hall, used today for major public ceremonial events such as lying in state, and the Jewel Tower.Control of the Palace of Westminster and its precincts was for centuries exercised by the Queen's representative, the Lord Great Chamberlain.  By agreement with the Crown, control passed to the two Houses in 1965. Certain ceremonial rooms continue to be controlled by the Lord Great Chamberlain.

After a fire in 1834, the present Houses of Parliament were built over the next 30 years. They were the work of the architect Sir Charles Barry  (1795–1860) and his assistant Augustus Welby Pugin  (1812–52). The design incorporated Westminster Hall and the remains of St Stephen's Chapel.