London is the capital of the United Kingdom. Its territorial extension makes it the third largest city in Europe. The metropolitan area has around 14 million residents and extends for several tens of kilometers along the Thames valley, up to its wide estuary. Many Londoners come from abroad or are of foreign origin, making it one of the most cosmopolitan and multi-ethnic cities in the world. London was the capital of the British Empire and therefore a destination for migratory flows during and especially after the end of the colonial era. It has the highest GDP among all European cities and the fifth in the world.

Together with New York it is part of the Alpha++ category, which places them as the two most important cities for the global economy. Numerous international institutions, organizations and companies are based in London. There are important museums and theaters there; the city contains four world heritage sites. Furthermore, the monarch of the United Kingdom permanently resides at Buckingham Palace, and the Palace of Westminster hosts the Parliament; Number 10 Downing Street is the residence of the Prime Minister and the seat of the Government of the United Kingdom.