Unlike the Underground, which is a single system owned and operated by Transport for London, commuter railways in London are run by a number of separate train operating companies (TOCs).
This results from the privatisation of British Rail in the 1990s which split the former state railway operator British Rail into a number of smaller franchises in order to increase competition and allow railways to operate in a free market.

Among the rail firms operating passenger services in London, a number are owned by foreign companies or by state-owned railways of other European countries.
London Overground is contracted in a different way to other franchises in that it is operated by a private company under contract to Transport for London.
Heathrow Express is also unusual in that it is not officially part of the National Rail franchising system.
Unlike the Underground, which is a single system owned and operated by Transport for London, commuter railways in London are run by a number of separate train operating companies (TOCs). This results from the privatisation of British Rail in the 1990s which split the former state railway operator British Rail into a number of smaller franchises in order to increase competition and allow railways to operate in a free market.
Among the rail firms operating passenger services in London, a number are owned by foreign companies or by state-owned railways of other European countries. London Overground is contracted in a different way to other franchises in that it is operated by a private company under contract to Transport for London. Heathrow Express is also unusual in that it is not officially part of the National Rail franchising system.
Transport in London