Coordinates: 51°34′54″N 2°42′57″W / 51.5818°N 2.7157°W / 51.5818; -2.7157

Sudbrook is a village in Monmouthshire, south east Wales. It is located 4 miles south west of Chepstow and 1 mile east of Caldicot. It lies close to the Second Severn Crossing on the Severn Estuary, and adjoins the village of Portskewett. It was largely built in the late 19th century for workers on the Severn railway tunnel. At that time it was also known as Southbrook.

Sudbrook was of early historic importance in guarding the Severn estuary at an ancient ferry crossing place. An Iron age hillfort is located on the coast, probably built and occupied by the Silures from the 2nd century BC and occupied by the Romans from the 1st century AD until the 4th century. The hillfort was originally much bigger than now having been eroded over the centuries. Finds of Roman coins at Black Rock, Portskewett, show that the ferry crossing was in use in Roman times, on the route between the Roman stations of Aquae Sulis (Bath) and Venta Silurum (Caerwent).

Monmouthshire (Welsh: Sir Fynwy) is a county in south east Wales. The name derives from the historic county of Monmouthshire of which it covers the eastern 60%. The largest town is Abergavenny. Other major towns include Caldicot, Chepstow and Monmouth.

The historic county of Monmouthshire was formed from the Welsh Marches by the Laws in Wales Act 1535, bordering Gloucestershire to the east, Herefordshire to the northeast, Brecknockshire to the north, and Glamorgan to the west. The second Laws in Wales Act of 1542 enumerated the counties of Wales and excluded Monmouthshire – This led to ambiguity as to whether the county was part of Wales or England. Since local government changes in April 1974 the area has been placed definitively in Wales. The eastern and southern boundaries of the historic county and the current principal area are the same, along the River Wye and Severn estuary; however, the western two-fifths of the historic county are now administered by the other unitary authorities of Blaenau Gwent, Torfaen, Caerphilly and Newport. The administrative county of Monmouthshire, and associated lieutenancy were abolished in 1974 under the Local Government Act 1972. The area largely became part of the new local government and ceremonial county of Gwent.