The Nantlle Valley (Welsh: Dyffryn Nantlle) is an area in north Wales characterised by its large number of small settlements.
Around 80% of the population of the Nantlle Valley speak Welsh as their first language. Some of the communities came into being as a result of slate quarrying in the late eighteenth or early nineteenth centuries. There were a number of quarries in the valley, the largest being the Dorothea Quarry and Penyrorsedd. Although the major quarries are worked out, there remains demand for slate waste for garden decoration. The horse-drawn Nantlle Railway served the quarries from 1865 to 1963.
In 1991 Antur Nantlle Cyf was established as a community enterprise to work for the benefit of the Nantlle Valley and its surrounding area. The valley was also where Josie Russell and her father lived after the Russell murder case.