Penrhyndeudraeth (Welsh pronunciation: [pɛnr̥ɨnˈdeɨ̯draːɨ̯θ] ^ⓘ; lit. 'peninsula with two beaches'; or simply Penrhyn) is a small town and community in the Welsh county of Gwynedd. The town is close to the mouth of the River Dwyryd on the A487 nearly 3 miles (4.8 km) east of Porthmadog, and had a population of 2,150 at the 2011 census, increased from 2,031 in 2001. The community includes the villages of Minffordd and Portmeirion.

An older settlement of a few cottages at Upper Penrhyn was originally called Cefn Coch ('Red Ridge') and that name is perpetuated by the Penrhyndeudraeth primary school, which is known as Ysgol Cefn Coch; but the town proper is comparatively modern. The ground on which it stands was a malarial swamp encircling a huge stagnant pool.

The present town owes its existence as a commercial centre to a local landowner, David Williams of Castell Deudraeth near Minffordd, who in the mid-19th century drained the swamp and dried the pool and constructed many streets. Adopting a scheme of town planning evolved by the builder of Tremadog and his Italian craftsmen, Williams gave Penrhyndeudraeth broad streets and wide open spaces. The main square is a road junction with choice of four roads - one leading to the station, one to Porthmadog, one to Maentwrog and the other to Llanfrothen and the Pass of Aberglaslyn. Williams' daughter, Alice, built the first Institute Hall for one of the first British Women's Institutes in the country in Penrhyndeudraeth.

Prior to the many 19th century land reclamation projects (including The Cob at Porthmadog) and the building of the Ffestiniog Railway, both of which spurred economic growth, the few local inhabitants relied on agriculture and small-scale copper mining. Some men worked boats on the River Dwyryd, carrying slate from Maentwrog to the sea for export. Local women at that time gathered cockles in the estuary for sale in local markets. Penrhyndeudraeth is still known locally, especially by the people of Blaenau Ffestiniog and Porthmadog, as Penrhyn Cocos (or "Cockletown" in English).

Halfway between Penrhyndeudraeth and Minffordd, next to the Snowdonia National Park HQ, but standing apart, is Hendre Hall, where, in 1648, Humphrey Humphreys was born. He became Bishop of Bangor from 1689 to 1701 and then of Hereford. He died in 1712. One of the family carvings at the Holy Trinity Church Penrhyndeudraeth is of him. There is also an oak chest which Richard Humphreys gave to Llanfrothen Church while working as its warden in 1690.

The property named "Cae Ednyfed", between Penrhyndeudraeth and Minffordd, was once the property of Ednyfed Fychan, commander-in-chief to Llywelyn ap Iorwerth.

The town has not always been very religious. Early in the history of the Methodists, they established chapels, and fellowship meetings (seiadau) were established. There is a history of revivalists such as Daniel Rowland who held meetings at Tyddyn Isaf and the poet Dafydd Siôn Siâms who publicly cursed the new religion before himself being converted. He chastised the Methodists mercilessly before burning all their critical poetic works in a public bonfire in the village square. The Old Methodists' original communion chalice is to be seen in the National Library in Aberystwyth. The town was originally in two Anglican parishes, Llanfrothen and Llandecwyn. Holy Trinity church was built in 1858 and a new parish of Penrhyndeudraeth was created in 1897.

For 130 years, the explosives works were the economic backbone of the town. Historically, the population depended on employment offered by the slate industry at Blaenau Ffestiniog and the trade in raw materials through the busy harbour at Porthmadog.