Deganwy is a small town in the county borough of Conwy, North Wales. It is located south of Llandudno and to the east of Conwy, (which is on the opposite side of the River Conwy) and with which it forms the Conwy parish community. The township lies in the historic county of Caernarfonshire. Deganwy is in the ecclesiastical parish of Llanrhos, and has a Victorian Gothic church dedicated to All Saints.

Deganwy's most notable feature is Deganwy Castle, which, in the 6th century was the stronghold of Maelgwn Gwynedd, king of Gwynedd. Deganwy appears to have been the capital of Gwynedd at this time, but this was later moved to Aberffraw on Anglesey. The hill on which the castle was built was fortified many times over the centuries. It was the site of a Norman castle built around 1082 and occupied by Robert of Rhuddlan, and later by Llywelyn the Great and Llywelyn ap Gruffudd. The castle was later demolished by Edward I when Conwy Castle was built opposite so that only ruins remain today.

Deganwy has a railway station on the Llandudno branch line with an hourly train service, available on request, to and from Manchester and intermediate stations. The LNWR built at Deganwy a rail connected riverside quay and wharfs, largely for the purpose of exporting slate by coastal steamer. The slate was brought by rail from Blaenau Ffestiniog. A marina with its accompanying housing and five star hotel accommodation was established on the site of the former slate wharfs early in the 21st century.