The Chatham Main Line is a railway line in England between London Victoria, and Dover Priory and Ramsgate, travelling via Medway (of which the town of Chatham is part, hence the name).

Services to Cannon Street follow the route as far as St Mary Cray Junction where they diverge onto the South Eastern Main Line near Chislehurst.

Thameslink services to Luton run in parallel from Rainham to Rochester, diverging once across the River Medway at Rochester Bridge Junction onto the North Kent Line via Gravesend and Dartford.

A shuttle service operates on the Sheerness Line which starts at Sittingbourne.

Most services on the Line are run by Southeastern and Southern. Govia Thameslink Railway run some Thameslink services, the first starting from London Blackfriars and travelling via Denmark Hill on the Catford Loop, joining at Shortlands Junction, travelling to Swanley before heading to Sevenoaks. The second service starts from Kentish Town and also travels via the Catford Loop to Shortlands Junction, travelling to Bickley before heading off to Orpington. The final service starts at Luton and goes via London Bridge, Greenwich, Dartford and Gravesend to Rochester before terminating at Rainham in the bay platform 0.

While travelling between Bromley South and London Victoria, the trains can either travel on the main line, through Beckenham Junction, Herne Hill and Brixton, or via the Catford Loop Line, coming away from the main line at Shortlands Junction, travelling through Catford and Peckham Rye, and then just past Brixton it either picks up the Southeastern line all the way, or can follow the Southern (Atlantic) Line through Clapham High Street before crossing back over to the Southeastern Line to London Victoria. The hourly stopping service is now scheduled to run via Catford, additionally stopping at Denmark Hill.

The off-peak timetable consists of two trains per hour from Victoria, calling at Bromley South, Longfield, Meopham, Rochester, Chatham, Gillingham and Rainham. One service will call at Newington, Sittingbourne, Teynham and Faversham, then all stations to Dover Priory via Canterbury East. The other service will just call at Sittingbourne and Faversham, then all stations to Margate and Ramsgate. These trains no longer split up at Faversham. There is an hourly service from Victoria calling at Denmark Hill via the Catford Loop, Bromley South, St Mary Cray then all stations to Gillingham. A High Speed Service sees two trains per hour from St Pancras International to Faversham via Gravesend and Chatham. One service terminates at Faversham before travelling back to St Pancras International via Chatham and Gravesend. The other service continues coastbound as a semi-fast service calling at Whitstable, Herne Bay, Birchington, Margate, Broadstairs and Ramsgate. It then carries on, stopping at Sandwich, Deal, Walmer, Martin Mill, Dover Priory, Folkestone Central, Folkestone West and Ashford International, before picking up the High Speed Line to Ebbsfleet International, Stratford International and arriving back at St Pancras International. A service operates in the opposite direction. There is one other High Speed Service that runs on a small part of the line, starting from Margate and calling at Broadstairs and Ramsgate before heading to Canterbury West, and Ashford International, then picking up the High Speed Line and calling at the remaining stations to St Pancras International. A Thameslink service now starts from Rainham and calls at nearly all stations via Strood, Gravesend, Dartford, Abbey Wood (for Elizabeth line services), Woolwich Arsenal and Greenwich (both for the Docklands Light Railway), London Bridge, Blackfriars and beyond. Passengers for Waterloo East, Charing Cross or Cannon Street now have to change at London Bridge.

The following trains are operated on the line : Class 465 "Networker" since 1992, Class 466 "Networker" since 1993, Class 375 "Electrostar" since 2001, Class 395 "Javelin" since 2009, and 8-car Class 700 "Desiro City" since 2018.