Thameslink, Southern and Great Northern (TSGN) is a management contract for the provision of passenger services on the Thameslink and Great Northern routes to Bedford, Luton, Peterborough, King's Lynn, Cambridge, London King's Cross, London Moorgate, Sutton, Wimbledon and Brighton, as well as the whole Southern network and the jointly operated First Capital Connect Southeastern services, which were added to the franchise on 25 July 2015, with the Southern and Gatwick Express brands retained.

Passenger rail franchising in Great Britain is the system of contracting the operation of the passenger services on the railways of Great Britain to private companies, which has been in effect since 1996 and was greatly altered in 2020, with rail franchising being effectively abolished in May 2021.