The Romney, Hythe and Dymchurch Railway (RH&DR) is a 15 in gauge light railway in Kent, England, operating steam and internal combustion locomotives. The 13+1⁄2-mile (21.7 km) line runs from the Cinque Port of Hythe via Dymchurch, St. Mary's Bay, New Romney and Romney Sands to Dungeness, close to the Dungeness nuclear power stations and Dungeness Lighthouse. The line is double track north of New Romney and single track south.

Fifteen-inch gauge railways were pioneered by Sir Arthur Percival Heywood who was interested in what he termed a minimum gauge railway for use as estate railways or to be easy to lay on, for instance, a battlefield. In 1874, he described the principle behind it as used for his Duffield Bank Railway, distinguishing it from a "narrow-gauge" railway. Having previously built a small railway of 9 in gauge, he settled on 15 in gauge as the minimum that he felt was practical.