Govia Thameslink Railway (GTR) is a train operating company that operates the Thameslink, Southern and Great Northern (TSGN) rail franchise in England. Within the franchise, GTR runs the Thameslink, Great Northern, Southern and Gatwick Express airport services.

GTR is a subsidiary of Govia, which is itself a joint venture between the British Go-Ahead Group (65%) and French company Keolis (35%).

Thameslink is a 24-hour, 115-station (32 managed) main-line route in the British railway system, running from Bedford, Luton, St Albans City, Peterborough and Cambridge via central London to Sutton, Orpington, Sevenoaks, Rainham, Horsham and Brighton. The network opened as a through service in 1988, with severe overcrowding by 1998, carrying more than 28,000 passengers in the morning peak