Since 1997 the United Kingdom government has been engaged in reforming the House of Lords, the upper house of the Parliament of the United Kingdom. The history of reform before 1997, is set out in sections below about reforms of composition and powers carried out in the past and of unsuccessful proposals and attempts at reform in the twentieth century. Proposals include decreasing the number of lords, introducing a system where lords are democratically elected, or abolition of the House of Lords in favour of a unicameral Parliament.

The House of Commons of England was the lower house of the Parliament of England (which incorporated Wales) from its development in the 14th century to the union of England and Scotland in 1707, when it was replaced by the House of Commons of Great Britain. In 1801, with the union of Great Britain and Ireland, that house was in turn replaced by the House of Commons of the United Kingdom.