The London commuter belt is the metropolitan area surrounding London, England from which it is practical to commute to work in the capital. It is alternatively known as the Greater South East, the London metropolitan area or the Southeast metropolitan area. It should not be confused with Greater London or the Greater London Urban Area.

The boundaries are not fixed; they expand as transport options improve and affordable housing moves further away from London. The commuter belt currently covers much of the South East region and part of the East of England region, including the Home Counties of Kent, Surrey, Berkshire, Buckinghamshire, Hampshire, Hertfordshire, Bedfordshire, Essex and Sussex. The population of Greater London and those counties adjacent to the green belt was 13,945,000 in 2001. Much of the undeveloped part of this area lies within the designated Metropolitan Green Belt. The Green belt currently covers nearly all of Surrey, eastern Berkshire, southern Buckinghamshire, southern and mid Hertfordshire, southern Bedfordshire, south-west Essex, and western Kent. In addition, three Areas of Outstanding Natural Beauty the Chiltern Hills, Surrey Hills and North Downs AONBs surrounding the Thames basin feature in the commuter belt.

London ⁱ/ˈlʌndən/ is the capital city of England and the United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium. London's ancient core, the City of London, largely retains its square-mile mediaeval boundaries. Since at least the 19th century, the name London has also referred to the metropolis developed around this core. The bulk of this conurbation forms the London region and the Greater London administrative area, governed by the elected Mayor of London and the London Assembly.

London is a leading global city, with strengths in the arts, commerce, education, entertainment, fashion, finance, healthcare, media, professional services, research and development, tourism and transport all contributing to its prominence. It is the world's leading financial centre alongside New York City and has the fifth-largest city GDP in the world (and the largest in Europe). London has been described as a world cultural capital. It was the world's most visited city during 2011 and London Heathrow is the world's busiest airport by number of international passengers. London's 43 universities form the largest concentration of higher education in Europe. In 2012 London will become the first city to host the modern Summer Olympic Games three times.

The term metropolitan area refers to a region consisting of a densely populated urban core and its less-populated surrounding territories, sharing industry, infrastructure, and housing. A metropolitan area usually comprises multiple jurisdictions and municipalities: neighborhoods, townships, cities, exurbs, counties, and even states. As social, economic and political institutions have changed, metropolitan areas have become key economic and political regions.

A metropolitan area combines an urban agglomeration (the contiguous, built-up area) with zones not necessarily urban in character, but closely bound to the center by employment or other commerce. These outlying zones are sometimes known as a commuter belt, and may extend well beyond the urban zone, to other political entities. For example, El Monte, California is considered part of the Los Angeles' metro area.

In practice, the parameters of metropolitan areas, in both official and unofficial usage, are not consistent. Sometimes they are little different from an urban area, and in other cases they cover broad regions that have little relation to a single urban settlement; comparative statistics for metropolitan area should take this into account. Population figures given for one metro area can vary by millions, and there is a tendency for people to promote the highest figure available for their own "city". However the most ambitious metropolitan area population figures are often better seen as the population of a "metropolitan region" than of a "city".^{[citation needed]}