John Ellis Caerwyn Williams FBA (17 January 1912 – 10 June 1999), was a Welsh scholar. His fields of study included the literatures of the Celtic languages, especially Welsh and Irish literature. He has published books in both English and Welsh.

Caerwyn Williams was born in Gwauncaegurwen, Glamorgan in 1912 into a coal-mining family. He studied at the University College of North Wales, Bangor and graduated in Latin in 1933 and in Welsh in 1934. He then studied further at University College, Dublin and Trinity College, Dublin. Intending to become a minister in the Presbyterian Church of Wales he studied at the United Theological College, Aberystwyth and graduated BD in 1944. In 1945 he was appointed to teach at the Department of Welsh at the University College of North Wales, Bangor and became professor of Welsh in 1953. He remained in that post until his appointment as professor of Irish at the University College of Wales, Aberystwyth in 1965, where he remained until his retirement in 1979. He was elected a Fellow of the British Academy in 1978. In 1971 he delivered the British Academy's Sir John Rhŷs Memorial Lecture.