Anglesey (Welsh: Ynys Môn), is an island and, as Isle of Anglesey, a county off the north west coast of Wales. Two bridges, spanning the Menai Strait, connect it to the mainland: the original Menai Suspension Bridge (carrying the A5), designed by Thomas Telford in 1826; and the more recently rebuilt Britannia Bridge (replacing the original designed by Robert Stephenson), which carries the A55 and the North Wales Coast Railway Line.

Historian and author John Davies argues that it was during the tumultuous 10th century that the Norse name for Môn, Anglesey, came into existence; the name was later adopted into English after Anglo-Norman occupiers arrived to conquer the island during the Norman invasions of Gwynedd.

The name Anglesey was later used in the English language as a county name which included Holy Island and other nearby small islands. About half of the inhabitants can speak, read and write Welsh as well as English, and 70% have a knowledge of Welsh.[3] Once the Welsh language was granted equal status in government with the Welsh Language Act of 1993, the representative constituency names for the island were changed to the Welsh name of the island, Ynys Môn (UK Parliament constituency) in the UK parliament, and Ynys Môn (Assembly constituency) in the National Assembly for Wales.

With an area of 714 square kilometres (276 sq mi),[4] Anglesey is the largest Welsh island, the sixth largest surrounding the island of Great Britain, and the largest island in the Irish Sea ahead of the Isle of Man.