Maelienydd, sometimes spelt Maeliennydd, was a cantref and lordship in east central Wales covering the area from the River Teme to Radnor Forest and the area around Llandrindod Wells. The area, which is mainly upland, is now in Powys. During the Middle Ages it was part of the region known as Rhwng Gwy a Hafren () and its administrative centre was at Cefnllys Castle.