Ysgol Gyfun Gymraeg Glantaf is a Welsh-medium secondary school in Llandaff North, a district in the north of Cardiff, Wales.

The name 'Glantaf' means 'The bank of the river Taf' in Welsh. Of the three Welsh-medium secondary schools serving Cardiff, it was the first to be established (the others being Ysgol Gyfun Gymraeg Plasmawr and Ysgol Gyfun Gymraeg Bro Edern). Although all students speak Welsh and normally have received Welsh-language primary education, a large percentage come from homes where Welsh is not the first language.

Ysgol Gyfun Gymraeg Glantaf was founded in 1978, initially sharing premises with the English-language Glantaf High School, before expanding to occupy the entire building. Its first Headmaster was Mr. J E Malcolm Thomas, who was succeeded upon his retirement in 1995 by Mr. Huw S Thomas, and then by Mrs. Rhiannon Lloyd. Since September 2010 Mr Alun Davies has been the Headteacher.

Ysgol Gyfun Gymraeg Glantaf is a Welsh-medium school, which means that all lessons except English Language and Literature take place in the Welsh language. The social use of Welsh is also highly encouraged, in order to ensure the pupils' fluency in the language.

The school's motto is Coron Gwlad Ei Mamiaith, which translates to 'A Country's Crown is Her Mother Tongue'. The school colours are light and dark blue.

The school's four houses are named after Welsh saints: Dewi (house colour: yellow), Dyfrig (green), Illtud (red) and Teilo (blue). The four houses annually compete in many competiions eg Eisteddfod, sports etc.