South West Trains (SWT) is a train operating company operating in the United Kingdom, providing train services to the south-west of London, chiefly in Greater London and the counties of Surrey, Hampshire, Dorset, Devon, Somerset, Berkshire and Wiltshire (the area largely covered before 1923 by the London and South Western Railway company, hence the new company's name).

Legally known as Stagecoach South Western Trains Limited, the parent company of SWT is Stagecoach Group which also owns 49% of the Virgin Trains Franchise. The SWT franchise is stated as being the most complicated train operating company to operate because of the vast number of services which are stated below. Since 2007, its sister company is East Midlands Trains.