The Rhymney Valley is a valley in South Wales, formerly famous for its coal mining and iron industries.
Created as a glacial valley, now the Rhymney River flows largely south to Rumney, a district of Cardiff. The river is the border between the traditional counties of Glamorgan and Monmouthshire.
This valley is one of the South Wales Valleys, and its history largely follows theirs: sparsely populated until the nineteenth century; industrialised for iron, steel and coal; industrial decline in the 1980s and 1990s.
The 1990s brought improved road connections to the valley - a dual carriageway running north from Caerphilly - increasing access to and from Cardiff and the M4 motorway, and increasing the numbers of commuters from the valley to Cardiff. The area is now one of the most populous in Wales.
The Rhymney Valley hosted the National Eisteddfod in 1990.
The Rhymney Valley railway runs through the valley.