The Lymington Branch Line is the railway line from Brockenhurst to Lymington. At Brockenhurst, trains connect with the South Western Main Line for mainline services to Bournemouth, Weymouth, Southampton and London Waterloo. At Lymington, the train connects with the ferry to Yarmouth on the Isle of Wight. Services operated on this line are often called the "Lymington Flyer".

The Lymington branch is electrified at 750 V DC third-rail, and has three stations. The first is Brockenhurst , where trains depart from a bay platform. The next station is Lymington Town , followed shortly afterwards by Lymington Pier , where the line terminates.

Services on the line are currently operated by South West Trains, using stock outbased at Bournemouth depot. Stock used is currently restricted to Classes 411, 412, 421 and 423. Newer stock cannot yet be used on the line until the electrical supply has been upgraded.

In recent years, a dedicated unit has been allocated to the "Lymington Flyer". As Lymington Town station has short platforms, the unit used has been reduced to three carriages from the standard four car length. The staff at Bournemouth depot have unofficially named each unit, details of which are given below. Units are listed in chronological order.

It was expected that by May 2005 at the latest, the operation of the line will be taken over by the new Class 450 "Desiro" units. However, it now seems that South West Trains will instead refurbish two 3Cig units that will be dedicated to services on the line. Work to the units will the include fitting of central door locking and other safety features, to allow them to remain in service beyond the November 2005 deadline for the withdrawal of slam-door stock.