The Western Region was a region of British Railways from 1948. The region ceased to be an operating unit in its own right on completion of the "Organising for Quality" initiative on 6 April 1992. The Region consisted principally of ex-Great Western Railway lines, minus certain lines west of Birmingham, which were transferred to the London Midland Region in 1963 and with the addition of all former Southern Railway routes west of Exeter, which were subsequently rationalised.

The Great Western Railway (GWR) was a British railway company that linked London with the southwest, west and West Midlands of England and most of Wales. It was founded in 1833, received its enabling act of Parliament on 31 August 1835 and ran its first trains in 1838 with the initial route completed between London and Bristol in 1841. It was engineered by Isambard Kingdom Brunel, who chose a broad gauge of 7 ft —later slightly widened to 7 ft 1⁄4 in —but, from 1854, a series of amalgamations saw it also operate 4 ft 8+1⁄2 in standard-gauge trains; the last broad-gauge services were operated in 1892.