Signalling on British Railways underwent massive change from Nationalisation in 1948 to privatisation in the 1990s, but throughout this period much of the network's infrastructure dated from the era of the Big Four and the pre-Grouping companies. The variety of traditional signalling in use in the BR era, from the pre-Grouping infrastructure and mechanical signalling up to BR-built signal boxes prior to the conversion to colour-light signalling, is explored here. The principles of signalling operation are also explained. In this book author Robert Hendry presents a fascinating insight into traditional signalling on British railways through a wealth of rare and previously unpublished images.