It is the only English region with a directly elected mayor with wide ranging devolved powers and an elected regional assembly which together comprise the Greater London Authority (the "GLA"). The current Mayor of London is Ken Livingstone. He is scrutinised by an elected London Assembly, which may amend his annual budget (by two-thirds majority) but otherwise lacks the power to block his directives. The headquarters of the GLA is at City Hall in Southwark. The Mayor is responsible for London's strategic planning and is required to produce a London Plan document.

For elections to the London Assembly, London is divided into fourteen constituencies. The constituencies are formed from the area of two or three boroughs combined. The City of London forms part of the City and East constituency.

Although the London County Council had been created as a London-wide authority covering the County of London in 1889, the County did not even cover all the built-up area of London then, particularly West Ham and East Ham; furthermore many of the LCC housing projects, including the vast Becontree Estate, were constructed outside its formal boundaries.

London County Council pressed for an alteration in its boundaries soon after the end of the First World War, noting that within the Metropolitan and City Police Districts there were 122 housing authorities. A Royal Commission was set up to consider the issue. London County Council proposed a vast new Greater London, somewhere between the Metropolitan Police District and the entire Home Counties. Protests were made at the possibility of including Windsor, Slough and Eton in the authority.

The Commission made its report in 1923, rejecting the LCC's scheme. Two minority reports favoured change beyond the amalgamation of smaller urban districts, including both smaller borough councils and a Central Authority for strategic functions. The London Traffic Act 1924 was a result of the Commission.

Greater London was formally created by the London Government Act 1963, which took force on 1 April 1965, replacing the former administrative counties of Middlesex and London, adding the City of London, which was not under the London County Council, and absorbing parts of Kent, Surrey, Essex and Hertfordshire. The term 'Greater London' had been used well before 1965, particularly to refer to the area covered by the Metropolitan Police District or the London Passenger Transport Area and by 1958 an area somewhat larger than the current region had been defined by the Registrar General as the Greater London Conurbation.

The population on the current territory of Greater London rose from about 1.1 million in 1801 (back then only about 0.85 million people were in the urban area of London, while 0.25 million were living in villages and towns not yet part of London) to an estimated 8.6 million in 1939, but declined to 6.8 million around 1980, before starting to rebound in the beginning of the 1980s. As of 2003, the population in Greater London has only recovered the level of the beginning of the 1970s (which was also the level of population in 1921). Some researchers expect the population of Greater London to reach 8.15 million by 2016, which would still be 0.45 million short of the 1939 peak.

Figures here are for Greater London in its 2001 limits. Figures before 1971 have been reconstructed by the Office for National Statistics based on past censuses in order to fit the 2001 limits. Figures from 1981 onward are midyear estimates (revised as of 2004), which are more accurate than the censuses themselves, known to underestimate the population of London.