The Steyning Line was a railway branch line that connected the West Sussex market town of Horsham with the port of Shoreham-by-Sea, with connections to Brighton. It was built by the London, Brighton and South Coast Railway, and opened in 1861. It was 20 miles in length. It followed the course of the River Adur for much of its extent and was alternatively known as the Adur Valley Line.

The Sutton and Mole Valley lines were constructed between 1847 and 1868 by the London, Brighton and South Coast Railway, the London and South Western Railway and the LBSCR-sponsored Horsham, Dorking and Leatherhead Railway.