The disruption will affect services between East Croydon, Gatwick Airport, Redhill and parts of Surrey and Sussex over the next three weekends, including Saturday, January 10 and Sunday, January 11.
The affected weekends also include Saturday, January 17 and Sunday, January 18, and Saturday, January 24 and Sunday, January 25.
All lines in the area will be closed as Network Rail carries out a series of major infrastructure upgrades.
Passengers travelling between London and Gatwick Airport will need to take a train to East Grinstead and then use replacement buses to reach the airport.
Alternatively, Southern will operate direct trains between London Victoria and Gatwick via an alternative route, but journeys will take much longer.
Those travelling between London and the south coast will need to take a train to East Grinstead and then use replacement buses to Three Bridges, where onward services to Brighton, Horsham, Littlehampton, Ore and Portsmouth will be available.
Replacement bus services will also be in place for routes through Surrey, including Redhill and Reigate, as well as for journeys between Redhill and Tonbridge.
Trains will run on the Caterham and Tattenham Corner lines on the affected Saturdays.
On Sundays, replacement buses will operate on the Tattenham Corner line, and ticket acceptance will be in place on local buses for the Caterham line.
The engineering work is part of a wider programme to upgrade infrastructure between East Croydon and Gatwick Airport.
Passengers are being warned that all journeys between London and Gatwick will take much longer and are being urged to allow extra time to reach the airport.
