Ysgol Gyfun Cwm Rhymni, translated to English as Rhymney Valley Comprehensive School, is a Welsh-medium school located in the village of Fleur-de-Lys in the Rhymney Valley. Cwm Rhymni was founded in 1981 with just over 100 pupils and has since grown to over 2000 pupils.

Cwm Rhymni was originally situated on two sites, a Lower school for years 7 and 8 and an Upper school for years 9 to 13, situated in Aberbargoed and Bargoed respectively. In the late 1990s the school was granted permission to build a new state of the art one-site building in Fleur-de-lys, which opened in 2002. The original Headmaster of Cwm Rhymni was Mr Huw Thomas, who was succeeded by Mr Hefin Mathias in 1995. Mr Mathias was in turn succeeded upon his retirement in 2008 by Mr Owain ap Dafydd, who continues to be teh schools Head Master today.

Ysgol Gyfun Cwm Rhymni has a strong reputation in relation to sports, especially in rugby and athletics. The school has also fared very well in the Urdd Eisteddfod.

The school's four houses are named after Welsh saints: Mabon (yellow), Cadog (green), Tudful (purple) and Sannan (blue). Tudful was a later addition to the original three houses as the school's numbers grew in the early 1990s. In 2009, a new house, Ilan, was also created in addition to the previous four houses because of the growing number of students.