part of the city and county of Cardiff, historic county of Glamorgan (Morgannwg), Wales. Formerly a separate town, Llandaff lies along the west bank of the River Taff about 2 miles (3 km) northwest of Cardiff's city centre.

The cathedral of the ancient diocese of Llandaff in the Church in Wales originated in a 6th-century foundation by the Celtic St. Teilo, but the present structure was begun by Bishop Urban in the early 12th century. The Book of Llandaff, compiled under Bishop Urban, was a record of privileges and grants made to the see in recognition of its ecclesiastical status. The cathedral lost a great deal of its revenue after the Reformation and fell into decay; in the 18th century the southwest tower and part of the roof collapsed, and a small church was erected inside the ruins. Considerable restoration of the original building occurred during the 19th century and, again, following severe damage in an air raid in World War II. Sir Jacob Epstein's statue Christ in Majesty dominates the nave. An annual music festival is held in the cathedral.

Llandaff Castle, the home of the medieval bishops, was destroyed about 1403–04 by the Welsh insurgent leader Owen Glendower, but the ruined gatehouse remains. Nearby are the Cathedral School, a theological college, and Howell's School for Girls. Retaining much of a village atmosphere at its centre, Llandaff has become an attractive residential section of Cardiff.