The Greater London Authority (GLA), colloquially known by the metonym City Hall, is the devolved regional governance body of Greater London, England. It consists of two political branches: an executive Mayor and the 25-member London Assembly, which serves as a means of checks and balances on the Mayor. Since May 2016, both branches have been under the control of the London Labour Party. The authority was established in 2000, following a local referendum, and derives most of its powers from the Greater London Authority Act 1999 and the Greater London Authority Act 2007.

In the United Kingdom, devolution is the Parliament of the United Kingdom's statutory granting of a greater level of self-government to the Scottish Parliament, the Senedd, the Northern Ireland Assembly and the London Assembly and to their associated executive bodies: the Scottish Government, the Welsh Government, the Northern Ireland Executive and in England, the Greater London Authority and combined authorities.