Skenfrith Castle (Welsh: Castell Ynysgynwraidd) is a ruined castle in the village of Skenfrith in Monmouthshire, Wales. The fortification was established by the Normans in the wake of the invasion of England in 1066, to protect the route from Wales to Hereford. Possibly commissioned by William fitz Osbern, the Earl of Hereford, the castle comprised earthworks with timber defences. In 1135, a major Welsh revolt took place and in response King Stephen brought together Skenfrith Castle and its sister fortifications of Grosmont and White Castle to form a lordship known as the "Three Castles", which continued to play a role in defending the region from Welsh attack for several centuries.
At the end of the 12th century, Skenfrith was rebuilt in stone. In 1201, King John gave the castle to a powerful royal official, Hubert de Burgh. During the course of the next few decades, it passed back and forth between several owners, including Hubert, the rival de Braose family, and the Crown. Hubert levelled the old castle and built a new rectangular fortification with round towers and a circular keep. In 1267 it was granted to Edmund, the Earl of Lancaster, and remained in the hands of the earldom, and later duchy, of Lancaster until 1825.