Anglesey (Welsh: Ynys Mon) is a large island just off the Northwest coast of Wales, separated from the mainland by the Menai Straits, which are crossed by the Menai Bridge, designed by Isambard Kingdom Brunel. To the West of Anglesey is the smaller Holy Island, on which is Holyhead, an important Irish Sea transport hub.
Comparatively flat by Welsh standards, the island is the site of Beaumaris Castle and the village of Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch, which has an outstandingly long name. Other major municipalities on the island are Llangefni, Benllech, and Amlwch, a centre for copper mining.
Anglesey was known in the Middle Ages as Mon Mam Cymru, the 'Mother of Wales' as it was the breadbasket of North Wales at the time.
In Roman times, the island was a centre of Druidry.