Hay Castle () is a medieval fortification and 17th-century mansion house in the small town of Hay-on-Wye in Powys, Wales. Originally constructed as part of the Norman invasion of Wales, the castle was designed as a ringwork overlooking the town in either the late-11th or early-12th centuries. It was rebuilt in stone around 1200 by the de Braose family and then had a turbulent history, being attacked and burnt several times during the First and Second Barons' Wars, the wars with the Welsh princes, the rebellion of Owain Glyndŵr and the Wars of the Roses. In the 17th century a Jacobean mansion house was built alongside the medieval keep and the property became a private home. Serious fires in 1939 and 1977 gutted the castle and, despite repairs in the 1980s, by the 21st century much of the building was derelict and unstable. Since 2011 it has been owned by the Hay Castle Trust who plan to renovate the property to form an arts and education centre.