The Metropolitan Railway was a railway that served London from 1863 to 1933, its mainline heading north from the capital's financial heart in the City to what were to become the Middlesex suburbs. Its first line connected the mainline railway termini at Paddington, Euston and King's Cross to the City. This was built beneath the New Road using the "cut-and-cover" method between Paddington and King's Cross and in tunnel and cuttings beside Farringdon Road from King's Cross to Smithfield, near the City. When, on 10 January 1863, this line opened with gas-lit wooden carriages hauled by steam locomotives, it was the world's first underground railway.
The railway was soon extended from both ends and northwards via a branch from Baker Street. It reached Hammersmith in 1864, Richmond in 1877 and completed the Inner Circle in 1884, but the most important route became the line north into the Middlesex countryside, where it stimulated the development of new suburbs. Harrow was reached in 1880, and the line eventually extended as far as Verney Junction in Buckinghamshire, more than 50 miles (80 kilometres) from Baker Street and the centre of London.
Electric traction was introduced in 1905 and by 1907 electric multiple units operated most of the services, though electrification of outlying sections did not occur until decades later. Unlike other railway companies in the London area, the Met developed land for housing and after World War I promoted housing estates near the railway with the "Metro-land" brand. On 1 July 1933, the Metropolitan Railway was amalgamated with the underground railways of the Underground Electric Railways Company of London and the capital's tramway and bus operators to form the London Passenger Transport Board.
Today, former Metropolitan Railway tracks and stations are used by the London Underground's Metropolitan, Circle, District, Hammersmith & City, Piccadilly and Jubilee lines, and by Chiltern Railways.