Wales is sometimes called the "castle capital of the world" because of the large number of castles in a relatively small area. Wales had about 600 castles, of which over 100 are still standing, either as ruins or as restored buildings. The rest have returned to nature, and today consist of ditches, mounds, and earthworks, often in commanding positions. Many of the sites in Wales are cared for by Cadw, the Welsh government's historic environment service.

The four castles of Beaumaris, Caernarfon, Conwy, and Harlech together make up the Castles and Town Walls of King Edward in Gwynedd World Heritage Site, considered to be the "finest examples of late 13th century and early 14th century military architecture in Europe".