Like Aberconwy and Ynys Mon, Arfon is a UK Parliamentary and Welsh Assembly constituency. The Assembly seat was first contested in the 2007 Welsh Assembly elections, whilst the Parliamentary seat was first contested in 2010. Arfon was a Plaid Cymru/Labour marginal seat at the last Parliamentary and Assembly elections.
The constituency was created from the former Caernarfon and Conwy constituencies and is based around the boundaries of the former Arfon District Council area. The two main population centres of the constituency are the university City of Bangor and the royal Town of Caernarfon.
Arfon constituency sits within Gwynedd (a Welsh principal authority) and is made up of the following electoral divisions: Arllechwedd, Bethel, Bontnewydd, Cadnant, Cwm y Glo, Deiniol, Deiniolen, Dewi, Garth, Glyder, Groeslon, Hendre, Hirael, Llanberis, Llanllyfni, Llanrug, Llanwnda, Marchog, Menai (Bangor), Menai (Caernarfon), Ogwen, Peblig, Penisarwaun, Pentir, Penygroes, Seiont, Talysarn, Tregarth and Mynydd Llandygai, Waunfawr and Y Felinheli.