London is the capital and largest city of England and the United Kingdom. It stands on the River Thames in south-east England at the head of a 50-mile (80 km) estuary down to the North Sea. It has been a major settlement for two millennia. The City of London, its ancient core and financial centre, was founded by the Romans as Londinium and retains boundaries close to its medieval limits. Since the late 19th century, "London" has also referred to the metropolis around this, historically split between the counties of Middlesex, Essex, Surrey, Kent and Hertfordshire, which today largely comprises Greater London,the region governed by the Greater London Authority. The City of Westminster, to the west of the City, has for centuries held the national government and parliament.

London as one of the world's major global cities exerts strong influence on the world's arts, commerce, education, entertainment, fashion, finance, health care, media, tourism and transportation. With a GDP of €801.66 billion in 2017, It is the biggest urban economy in Europe. and one of the largest financial centres in the world – in 2019 with the second highest number of ultra high-net-worth individuals in Europe after Paris. In 2020 London had the second-highest number of billionaires of any city in Europe after Moscow. It has Europe's largest concentration of higher education institutions, including Imperial College London in natural and applied sciences, the London School of Economics in social sciences, and the comprehensive University College London. In 2012, London became the first city to host three modern Summer Olympic Games.