The Cuckoo Line is an informal name for the now defunct railway service which linked Polegate and Eridge in East Sussex, England, from 1880 to 1968. It was nicknamed the Cuckoo Line by drivers, from a tradition observed at the annual fair at Heathfield, a station on the route. At the fair, which was held each April, a lady would release a cuckoo from a basket, it being supposedly the 'first cuckoo of spring'. The railway line served the following Sussex communities: Polegate, Hailsham, Hellingly, Horam for Waldron, Heathfield, Mayfield, Rotherfield and Eridge. Services continued through Eridge and onward via Groombridge to Tunbridge Wells.

Polegate is a town and civil parish in the Wealden District of East Sussex, England, United Kingdom. It is located five miles (8 km) north of the seaside resort of Eastbourne and is part of the greater area of that town. Although once a railway settlement, its rail links were closed as part of the Beeching cuts. The 2011 census put the civil parish of Polegate at a population of 8,586, with 41.2% aged 65 and over.