The River Taff is a river in South Wales.

It rises as two rivers in the Brecon Beacons - the Taff Fechan (Little Taff) and the Taff Mawr (Big Taff), before joining to form the Taff north of Merthyr Tydfil. At Abercynon, it is joined by the Cynon river, and at Pontypridd it is joined by the Rhondda river. From Pontypridd, it runs roughly southerly through Taff's Well and Radyr, before arriving at the city of Cardiff in Llandaff.

In Cardiff, the river runs through Bute Park and next to the former Cardiff Arms Park, now the Millennium Stadium.

The term "Taffy" used as a nickname to people from Cardiff and by extension to all of South Wales, and all Welshmen, originates from the name of the river. It may be seen as slightly derogatory.