Ynystawe (also Ynysdawe in Welsh; Welsh pronunciation: [ənɨ̞s.taʊ.ɛ]) is a small village in the City and County of Swansea in Wales, in the electoral ward of Morriston. It is centred half a mile (1 km) north of Junction 45 of the M4 motorway, between Ynysforgan and Clydach in the lower Swansea Valley. The Welsh name Ynystawe or Ynysdawe derives from ynys, meaning "island" or "river-meadow", and Tawe, the name of the river running immediately to the east and which gives the Welsh name of Swansea, Abertawe.
The village occupies the steep south-east lower slopes of otherwise largely green Mynydd Gelliwastad, a steep hill, as well as the narrowest section of alluvial plain on the western side of the lower Swansea Valley. The lower plateau of Mynydd Bach, and Swansea Bay, can be viewed from its summit. The village is built around the B4063 road, towards neighbouring Clydach to its north-east, with a few houses on a contour road 70 metres higher. The river Tawe is diverted westwards below the village by the Glais moraine. This is a rare crescentic terminal moraine left over from the southern edge of the ice sheet from the last glaciation (about 10,000 years ago), and can be seen from the upper parts of the village as a distinctive elevation of the valley floor.
In Ynystawe Park there stands a memorial stone to Hopcyn ap Tomos (ap Einion) of Ynystawe (c. 1330-1408). Tomos was a learned man who commissioned the compilation of the Llyfr Coch (Red Book), which brought together most of the great Welsh literature of the time into a single volume. This included Cymric (Welsh) prose and poetry as well as the so-called Mabinogion tales. The Llyfr Coch is considered to be the most complete and impressive collection of Cymric literature, and is housed in the University of Oxford's Bodleian Library.