The Vale of Grwyney is a community in Powys, Wales. It follows most of the border between Powys and Monmouthshire. It takes its name from the river Grwyney which flows through it into the River Usk. The river Grwyney has two tributaries, called the Grwyne Fechan and the Grywne Fawr, which both rise in the Black Mountains and converge into one river near Llanbedr before meeting the Usk at Glangrwyney.