The railway system of Great Britain started with the building of local isolated wooden wagonways starting in the 1560s. A patchwork of local rail links operated by small private railway companies developed in the late 18th century. These isolated links expanded during the railway boom of the 1840s into a national network, although initially being run by over one hundred competing companies. Over the course of the 19th and early 20th centuries, many of these were amalgamated or were bought by competitors until only a handful of larger companies remained. The period also saw a steady increase in government involvement, especially in safety matters, such as the Railway Inspectorate.

The history of rail transport in Ireland began only a decade later than that of Great Britain. By its peak in 1920, Ireland had 3,500 route miles (5,630 km). The current status is less than half that amount, with a large unserviced area around the border area between Northern Ireland and The Republic of Ireland.