Ystrad Tywi (English: Vale of [the river] Tywi) is an area of south-west Wales situated on the banks of the Tywi river as it approaches the sea to join the Bristol Channel at Carmarthen. Although Ystrad Tywi was never a kingdom itself, it was a valuable territory and was fought over by the various kings of Dyfed, Deheubarth, Seisyllwg, the Kingdom of Gwynedd, the Kingdom of Morgannwg and the Normans.