Hafodyrynys is a village on the A472 road between Pontypool and Crumlin in Caerphilly county borough, south-east Wales. It lies within the historic boundaries of Monmouthshire.
The village is served by an inn, a takeaway, a rugby club and car wash/valet service. As of 2008 a new housing estate has been completed on the western periphery of the village.
Since 2017, the upward climb on the A472 through Hafodyrynys has been measured as Wales' most polluted road. In 2021, following extensive investigation and compulsory purchase of the affected properties, the terraced housing directly on the A472 was demolished due to the level of air pollution observed on the road.The village was served by the Taff Vale Extension of the Newport, Abergavenny and Hereford Railway. This ran from Pontypool to Crumlin and beyond. The 280-yard Glyn Tunnel in the village enabled the line to avoid the highest ground as it proceeded towards the Crumlin Viaduct, via Hafodyrynys Platform railway station to the west of the village. Passenger services ceased on 15 June 1964 as a result of the Beeching cuts, though coal traffic continued. Crumlin Viaduct was closed and then dismantled from 1967 onwards, resulting in coal from the colliery being extracted via the junction with the Ebbw Valley Railway.