Coordinates: The Sirhowy Valley (Welsh: Dyffryn Sirhywi) is an industrialised valley in the eastern part of the Valleys region of South Wales. It is named from the Sirhowy River (Welsh: Afon Sirhywi) which runs through it. Its upper reaches are occupied by the town of Tredegar within the unitary area of Blaenau Gwent. The valley initially heads south-southeast between the ridges of Cefn Manmoel to the east and Mynydd Bedwellte to the west before turning to a more southerly direction. Its central section is one of the least populated of the Welsh coalfield valleys. The valley enters the unitary area of Caerphilly which contains the towns of Blackwood (Welsh: Y Coed Duon) and Pontllanfraith. It then turns east and joins the valley of the Ebbw River, Ebbw Vale at Crosskeys.
The valley's industrial history began with ironworks before evolving to meet the demand for coal and the expansion of coal mining. This process was led by companies such as the Tredegar Iron and Coal Company. Coal mines used to be located throughout the valley, including: Wyllie; Nine Mile Point and Oakdale. The Sirhowy passes the old Gelligroes Mill near Blackwood along its path.
- Ordnance Survey 1:25,000 scale Explorer map sheets 152 Newport & Pontypool/Casnewydd a Phont-y-pŵl and 166 Rhondda & Merthyr Tydfil/Merthyr Tudful