St Fagans National Museum of History (/ˈfæɡənz/ FAG-ənz; Welsh: Sain Ffagan: Amgueddfa Werin Cymru), commonly referred to as St Fagans after the village where it is located, is an open-air museum in St Fagans, Cardiff, Wales, chronicling the historical lifestyle, culture, and architecture of the Welsh people. The museum is part of the wider network of Amgueddfa Cymru – Museum Wales.
It consists of more than forty re-erected buildings from various locations in Wales, and is set in the grounds of St Fagans Castle, a Grade I listed Elizabethan manor house. In 2011 Which? magazine named the museum the United Kingdom's favourite visitor attraction.