Signalling on British Railways underwent massive changes 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. In this book author Robert Hendry presents a photographic portrait of the variety of traditional signalling in use in the BR era, from the pre-Grouping infrastructure and mechanical signalling up to BR-built signalboxes prior to the conversion to colour-light signalling. The reader is also introduced to the principles of signalling operation.