Rhwng Gwy a Hafren (English: Between Wye and Severn) was a region of medieval Wales, located in the Welsh Marches between Powys to the north and Brycheiniog to the south. It was bounded by the rivers Wye (Welsh: Gwy) and Severn (Welsh: Hafren). It covered about the same territory as Radnorshire, now part of the county of Powys. The region first came into its own in the 9th or 10th centuries, when it was ruled by leaders who operated independently of the surrounding kingdoms.