Blaenau Ffestiniog is a town in Gwynedd, Wales. Once a slate mining centre in historic Merionethshire, it now relies much on tourists, drawn for instance to the Ffestiniog Railway and Llechwedd Slate Caverns. It reached a population of 12,000 at the peak development of the slate industry, but fell with the decline in demand for slate. The population of the community, including the nearby village Llan Ffestiniog, was 4,875 at the 2011 census: the fourth most populous in Gwynedd after Bangor, Caernarfon and Llandeiniolen. The population not including Llan is now only about 4,000.

Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism. It is the finest-grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression.