Torfaen (/tɔːrˈvaɪn/; [tɔrˈvaɪn]) is a county borough in the south-east of Wales. Torfaen is bordered by the county of Monmouthshire to the east, the city of Newport to the south, and the county boroughs of Caerphilly and Blaenau Gwent to the south-west and north-west. It is within the boundaries of the historic county of Monmouthshire, and between 1974 and 1996 was a district of Gwent, until it was reconstituted as a principal area in 1996.

Torfaen (meaning "breaker of stones") is an old name for the river – today called Afon Lwyd ("grey river") – which flows through the county borough from its source north of Blaenavon southward through Abersychan, Pontypool, and Cwmbran. The last three towns mentioned are a contiguous urban area.

The borough was formed in 1974 as a local government district of Gwent. It covered the whole area of three former districts and two parishes from another two districts, which were all abolished at the same time:

All the constituent parts of Torfaen had previously been in the administrative county of Monmouthshire prior to the reforms. Gwent County Council provided county-level services to the new borough.

Torfaen was reconstituted in 1996 as a county borough, taking over the county-level functions from the abolished Gwent County Council. The area is now governed by Torfaen County Borough Council, which is a principal council.

Torfaen has its own museum Torfaen Museum, in Pontypool Park, Pontypool.

The area has a population of around 91,000. Much of the southern part of the county borough around Cwmbran is extensively urban. The north of the county borough is greener and retains extensive areas of countryside, especially on the route to Blaenavon.

The administrative centre is Pontypool in the centre of the county borough. Most of the administration of Torfaen County Borough Council is conducted from Pontypool Civic Centre.