Undy is a village in Monmouthshire, south east Wales, adjoining the village of Magor with which it forms the community and parish of Magor with Undy. It is located about 3 miles west of Caldicot and 10 miles east of Newport, close to the junction of the M4 and M48 motorways, and adjoins the Caldicot Levels on the north bank of the Bristol Channel.