Ynys Môn (Welsh pronunciation: [ˌənɨs ˈmoːn]; officially called Anglesey until 1983) is a constituency of the House of Commons of the Parliament of the United Kingdom. It elects one Member of Parliament (MP) by the first past the post system of election. It is one of five 'protected constituencies' within the UK, with boundaries defined by the Parliamentary Constituencies Act 2020 to be fixed to those of Isle of Anglesey County Council.^[2]

The Ynys Môn Senedd constituency was created with the same boundaries in 1999 (as an Assembly constituency).

Ynys Môn is represented by Virginia Crosbie of the Conservative Party. Crosbie is the first Conservative to win the constituency since the 1983 general election.

The seat covers the isles of Anglesey and Holy Island. Incomes and house prices are slightly below average for the UK. Electoral Calculus describes the seat as "Traditionalist", characterised by socially conservative Labour-inclined voters with lower levels of income and formal education.^[3]

The Laws in Wales Act 1535 (26 Hen. 8. c. 26) provided for a single county seat in the House of Commons for each of 12 historic Welsh counties (including Anglesey) and two for Monmouthshire. Using the modern year, starting on 1 January, these parliamentary constituencies were authorised in 1536.

The Act contains the following provision, which had the effect of enfranchising the shire of Anglesey:

And that for this present Parliament, and all other Parliaments to be holden and kept for this Realm, one Knight shall be chosen and elected to the same Parliaments for every of the Shires of Brecknock, Radnor, Mountgomery and Denbigh, and for every other Shire within the said Country of Dominion of Wales;

The earliest known results are a fragment of the 1541 returns, in which the name of the Knight of the Shire for Anglesey (as Members of Parliament from county constituencies were known before the 19th century) has been lost.^{[4][5][6][7][8][9][10][11][12][13][excessive citations]} It is not known if Anglesey was represented in the parliaments of 1536 and 1539.^[14]

The borough constituency of Newborough, soon renamed Beaumaris, returned a member of parliament for the boroughs of Anglesey. It was abolished in 1885, leaving only the county constituency of Anglesey. The official name of the constituency in English was Anglesey, until it was replaced by the Welsh name Ynys Môn. Parliament approved the change, to take effect from the 1983 general election. This was purely an alteration of the official name, as no boundary changes were involved.

Geographically, the constituency of Ynys Môn comprises the whole of the main island of Anglesey and the smaller Holy Island.^[2]

The Parliamentary Constituencies Act 2020 amends Schedule 2 to the Parliamentary Constituencies Act 1986 in granting Ynys Môn "protected" status, meaning the boundaries of the constituency cannot be changed in future boundary reviews.

• Ynys Môn (Senedd constituency)
• List of parliamentary constituencies in Gwynedd
• List of parliamentary constituencies in Wales