The Menai Strait (Welsh:Afon Menai, the "River Menai") is a narrow stretch of shallow tidal water about 25 km (16 mi) long, which separates the island of Anglesey from the mainland of Wales.

The strait is bridged in two places – the main A5 road is carried over the strait by Thomas Telford's iron suspension bridge, the first of its kind, opened in January 1826, and adjacent to this is Robert Stephenson's 1850 Britannia Tubular Bridge. Originally this carried rail traffic in two wrought-iron rectangular box spans, but after a disastrous fire in 1970, which left only the limestone pillars remaining, it was rebuilt as a steel box girder bridge, and now carries both rail and road traffic. Between the two bridge crossings there is a small island in the middle of the strait, Ynys Gorad Goch, on which are built a house and outbuildings and around which are the significant remains of fish traps, no longer used.