The Metropolitan Line grew out of the Metropolitan Railway, one of the earliest Underground railways in the world. It's one of the furthest-reaching London Underground lines, as although its south-east end is just at the edge of the City of London, it extends into rural Buckinghamshire in the north-west. On a standard tube map, the Metropolitan Line is maroon or purple.

                Amersham   Chesham
                      |       |
Uxbridge    Chalfont and Latimer   Watford
  |                   |            /
  |                   \           /
Hillingdon      Chorleywood   Croxley
  |                     \       /
Ickenham       Rickmansworth   /
  |                       \   /
  |                        \ /
Ruislip                     v
  |                         |
  |                     Moor Park
  |                         |
Ruislip Manor           Northwood
  |                         |
Eastcote             Northwood Hills
  |                         /
Rayners Lane             Pinner
  \                       /
   \                 North Harrow
West Harrow            /
      \               /
     Harrow-on-the-Hill
              |
       Northwick Park
              |
        Preston Road
              |
        Wembley Park
              |
        Finchley Road
              |
        Baker Street
              |
    Great Portland Street
              |
        Euston Square
              |
   King's Cross St Pancras
              |
         Farringdon
              |
          Barbican
              |
          Moorgate
              |
       Liverpool Street
              |
           Aldgate

The Metropolitan Line is concurrent with the Piccadilly Line from Uxbridge to Rayners Lane; with the Jubilee Line from Wembley Park to Baker Street (with fewer stops); with the Circle Line from Baker Street to Aldgate; and with the Hammersmith and City Line from Baker Street to Liverpool Street.

Connections to the Bakerloo Line at Baker Street; to the Northern Line at King's Cross St Pancras and Moorgate; to the Piccadilly Line and Victoria Line at King's Cross St Pancras; and to the Central Line at Liverpool Street.

National Rail connections at Amersham, Chalfont and Latimer, Harrow-on-the-Hill, Euston Square for Euston, King's Cross St Pancras for King's Cross and St Pancras, Farringdon, Barbican, Moorgate and Liverpool Street.