The Great Western Railway (GWR) was a British Railway Company that linked London with the south west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835, and ran its first trains in 1838. It was engineered by Isambard Kingdom Brunel who chose a broad gauge of 7 ft 0+14 in (2,140 mm), but from 1854 a series of amalgamations saw it also operate 4 ft 8+12 in (1,435 mm) standard gauge trains; the last broad gauge services were operated in 1892. The GWR was the only company to keep its identity through the Railways Act 1921 which amalgamated it with the remaining independent railways within its territory, and it was finally wound up at the end of 1947 when it was nationalised and became the Western Region of British Railways.

The GWR was called by some "God's Wonderful Railway" and by others the "Great Way Round", but it was famed as the "Holiday Line", taking many people to resorts in South West England. In 1999, in recognition of the railway's historical importance, parts of the original Great Western Main Line were added to UNESCO's tentative World Heritage Sites list.

The company's locomotives, many of which were built in the company's workshops at Swindon, were painted a Brunswick green colour, while for most of its existence it used a two-tone "chocolate and cream" livery for its carriages. Wagons were painted red but this was later changed to mid-grey.

Great Western trains included long-distance express services such as the Flying Dutchman, the Cornish Riviera Express and the Cheltenham Spa Express. It also operated many suburban and rural services, some operated by steam railmotors or autotrains. The company pioneered the use of larger, more economic goods wagons than were usual in the United Kingdom. It operated a network of road motor (bus) routes, was a part of the Railway Air Services, and owned ships, docks and hotels.