Lydd is a town and electoral ward in Kent, England, lying on Romney Marsh. It is one of the larger settlements on the marsh, and the most southerly town in Kent. Lydd reached the height of its prosperity during the 13th century, when it was a corporate member of the Cinque Ports, a "limb" of Romney. Located on Denge Marsh, Lydd was one of the first sandy islands to form as the bay filled in and evolved into what is now called Romney Marsh.

The parish of Lydd comprises the town of Lydd, Dungeness, Lydd-on-Sea and parts of Greatstone-on-Sea.

Notable buildings in Lydd include the Gordon house longhall, a guildhall, and a medieval courthouse. Chamberlains and churchwardens' accounts of the 15th century survive alongside the town charters.

Lydd lies to the southwest of New Romney and east of Rye.

The place-name 'Lydd' is first attested in an Anglo-Saxon charter of 774, where it appears as ad Hlidum. This is the dative plural of the Old English hlid meaning 'slope'.

Lydd developed as a settlement on a shingle island during the Romano-British period, when the coast at the time cut off Lydd from the mainland.

The settlement continued into the Saxon period, when the Saxon church used Roman materials as part of its early construction. The town reached the height of its prosperity during the 13th century, when it was a corporate member of the Cinque Ports, a "limb" of Romney.

Together with sites in the marsh, the town was a base for smuggling in the 18th and 19th centuries. Lydd Guildhall, which originally accommodated some prison cells, dates to 1792.