The South West Main Line (SWML) is a 143-mile major railway line between Waterloo station in central London and Weymouth on the south coast of England. A predominantly passenger line, it serves many commuter areas including south western suburbs of London and the conurbations based on Southampton and Bournemouth. It runs through the counties of Surrey, Hampshire and Dorset. It forms the core of the network built by the London and South Western Railway, today mostly operated by South Western Railway.

Waterloo station, also known as London Waterloo, is a major central London terminus on the National Rail network in the United Kingdom, in the Waterloo area of the London Borough of Lambeth. It is connected to a London Underground station of the same name and is adjacent to Waterloo East station on the South Eastern Main Line. The station is the terminus of the South West Main Line to Weymouth via Southampton, the West of England main line to Exeter via Salisbury, the Portsmouth Direct line to Portsmouth Harbour which connects with ferry services to the Isle of Wight, and several commuter services around west and south-west London, Surrey, Hampshire and Berkshire.