Ceredigion is a parliamentary constituency represented in the House of Commons of the UK Parliament. Created in 1536, the franchise expanded in the late 19th century and on the enfranchisement of women. Its boundaries remained virtually unchanged until 1983. From 1536 until 1885 the area had two seats : a county constituency (Cardiganshire) comprising the rural areas, the other the borough constituency known as the Cardigan District of Boroughs comprising a few separate towns; in 1885 the latter was abolished, its towns and electors incorporated into the former, reduced to one MP. The towns which comprised the Boroughs varied slightly over this long period, but primarily consisted of Cardigan, Aberystwyth, Lampeter and Adpar, the latter now a suburb of Newcastle Emlyn across the Teifi, in Carmarthenshire.

Cardigan is a town and community in the county of Ceredigion, Wales. Positioned on the tidal reach of the River Teifi at the point where Ceredigion meets Pembrokeshire, Cardigan was the county town of the historic county of Cardiganshire. Cardigan is the second-largest town in Ceredigion. The largest town, Aberystwyth, is one of the two administrative centres; the other is Aberaeron.