London is the capital of England and the United Kingdom. It is the most populous city in the United Kingdom, with a population of over 13 million. Standing on the Thames, London has been a major settlement for two thousand years, its history going back to its Roman founding, which it named Londinium. The ancient city of London, the City of London, in particular, maintains its 2.9 km2 medieval borders and in 2011 had a population of 7,375; making it the smallest city in England. Since at least the 19th century, the name London has been applied to a larger city developed in this context. A large part of this area forms the administrative centre of Greater London (corresponding to the London region), which is controlled by the Mayor of London and the Council of London.

London is a world-class city, with a strong presence in the arts, commerce, education, entertainment, fashion, finance, health, media, professional services, research and development, tourism, and transportation. It is one of the world's leading financial institutions and has the fifth or sixth largest GDP in the world in terms of average. London is the cultural capital of the world. The most visited city in the world as it is measured by immigrants and has the largest airport system in the world measured by traffic congestion. The 43 universities of London form the largest educational institution in Europe. In 2012, London became the first city to host the modern Olympic Games three times.

London is a multicultural city, and more than 300 languages   are spoken in Greater London. The region had an official population of 8,416,535 in 2013, the largest municipality in the European Union, and accounted for 12.5%   of the UK population. London's suburbs are the second most populous in the EU, after Paris, with a population of 9,787,426 according to the 2011 census. The metropolitan area is third-most populous in Europe after Moscow and Istanbul; with a population of 13,614,409, and the Greater London Authority has a population of the London region 21 million. London was the most populous city in the world from about 1831 to 1925.

London has Four World Heritage Sites: Tower of London; Kew Gardens; an area that includes Westminster Palace, Westminster Abbey, and St Margaret Church; and Greenwich historic sites (where the Royal Observatory, Greenwich marks the Prime Meridian, 0 ° longitude, and GMT). Other world-famous landmarks include Buckingham Palace, London Eye, Piccadilly Circus, St Paul's Cathedral, Tower Bridge, Trafalgar Square, and The Shard. London is home to many museums, exhibitions, libraries, sporting events and other cultural canters, including the British Museum, National Gallery, Tate Modern, British Library and 40 West End theatres. London Underground is the oldest railway network in the world.