It is bordered by Cardiff to the southwest, Newport to the southeast, Torfaen to the east, Blaenau Gwent to the northeast, Powys to the north, Merthyr Tydfil to the northwest and Rhondda Cynon Taf to the west.

Some of the larger towns are Bedwas, Risca, Ystrad Mynach, Newbridge, Blackwood, Bargoed, New Tredegar and Rhymney.

The valley also includes the communities of Abertysswg, Fochriw, Pontlottyn, Tir-Phil, Brithdir, New Tredegar, Aberbargoed, Rhymney and Ystrad Mynach, and the towns of Bargoed and Caerphilly.

[4] Located on the edge of the South Wales Coalfield this area was sparsely populated with livestock husbandry being the main occupation.

At its peak before World War I, it was producing over a million tons of coal a year and employing nearly three thousand people.