The City of Westminster is a city and borough in Inner London which forms a core part of Central London. It is the site of the United Kingdom's Houses of Parliament and much of the British government. The city and borough's southern boundary is the Thames. It occupies a large area of central Greater London, including most of the West End. To the City of Westminster's east is the City of London and to its west is the Royal Borough of Kensington and Chelsea. To its north is the London Borough of Camden. Historically, Westminster was a part of the ceremonial county of Middlesex. Many London landmarks are within the borough, including Buckingham Palace, the Palace of Westminster (Houses of Parliament), Westminster Abbey, Whitehall, 10 Downing Street, and Trafalgar Square.

The borough is divided into a number of localities including the ancient political district of Westminster; the shopping areas around Oxford Street, Regent Street, Piccadilly and Bond Street; and the night-time entertainment district of Soho. Much of the borough is residential, and in 2008 it was estimated to have a population of 236,000. Aside from numerous large parks and open spaces, including Hyde Park and most of Regent's Park, the population density of the district is high.

The London Westminster borough was created with the 1965 establishment of Greater London. Upon the creation, it inherited the city status previously held by the then Metropolitan Borough of Westminster from 1900, which was first awarded to Westminster in 1540. The local government body is Westminster City Council.