Thameslink is a mainline route on the British railway network, running from Bedford, Luton, St Albans City, Peterborough, Welwyn Garden City, London Blackfriars and Cambridge via central London to Sutton, Orpington, Sevenoaks, Rainham, Horsham, Three Bridges, Brighton and East Grinstead. The network opened as a through service in 1988, with severe overcrowding by 1998, carrying more than 28,000 passengers in the morning peak. All the services are currently operated by Govia Thameslink Railway. Parts of the network, from Bedford to Three Bridges, run 24 hours a day, except on early Sunday mornings and during maintenance periods.

Blackfriars, also known as London Blackfriars, is a central London railway station and connected London Underground station in the City of London. It provides Thameslink services: local, and regional and limited Southeastern commuter services to South East London and Kent. Its platforms span the River Thames, the only one in London to do so, along the length of Blackfriars Railway Bridge, a short distance downstream from Blackfriars Bridge. There are two station entrances either side of the Thames, along with a connection to the London Underground District and Circle lines.