The Aldershot and Alton lines of the LSWR (the London and South Western Railway) were railways developed from 1849 onwards in the region in Surrey and Hampshire, England, between the Southampton main line and Guildford. First was a line from Guildford to Farnham, soon extended to Alton in 1852. The Reading, Guildford and Reigate Railway, an affiliate of the South Eastern Railway (SER), used part of that line by running powers. When the Aldershot Garrison and associated camps opened, suddenly Aldershot had a large population, both civilian and military, and the LSWR built a line from Pirbright Junction, on the Southampton main line. As well as serving Aldershot, this line gave a more direct route from London. It opened in 1870.
It was complemented by a short curve near Ash enabling trains from Guildford to reach Aldershot, opening in 1879. This formed an Aldershot loop that by-passed part of the original line, from Ash Junction through Tongham to Farnham Junction. Although the Tongham section retained a train service, the Aldershot route became dominant. In 1937 many of the lines in the area were electrified, but the Tongham section was closed to passenger traffic. Three routes extended from the west end of Alton station, the first being the Mid-Hants Railway in 1865. All three were conceived as important trunk routes and none fulfilled that potential. All were closed, the last closing in 1973.
The electrified network, Guildford via Aldershot to Farnham and Alton, and Pirbright Junction to Aldershot and Farnham Junction, continue in busy passenger use at the present day, together with a diesel passenger service over the Guildford to Reading route, which uses the original SER running powers section from Ash Junction to Aldershot South Junction.