Cardiff (; Welsh: Caerdydd [kairˈdiːð, kaːɨrˈdɨːð] (listen)) is the capital and largest city of Wales. It forms a principal area, officially known as the City and County of Cardiff (Welsh: Dinas a Sir Caerdydd), and the city is the eleventh-largest in the United Kingdom. Located in the south-east of Wales and in the Cardiff Capital Region, Cardiff is the county town of the historic county of Glamorgan and in 1974–1996 of South Glamorgan. It belongs to the Eurocities network of the largest European cities. A small town until the early 19th century, its prominence as a port for coal when mining began in the region helped its expansion. In 1905 it was ranked as a city and in 1955 proclaimed capital of Wales. Cardiff Built-up Area covers a larger area outside the county boundary, including the towns of Dinas Powys and Penarth.

Cardiff is the main commercial centre of Wales as well as the base for the Senedd. At the 2021 census, the unitary authority area population was put at 362,400. The population of the wider urban area in 2011 was 479,000. In 2011 it ranked sixth in the world in a National Geographic magazine list of alternative tourist destinations. It is the most popular destination in Wales with 21.3 million visitors in 2017.

Cardiff is a major centre for television and film production (such as Doctor Who, Torchwood and Sherlock) and is the Welsh base for the main national broadcasters.

Cardiff Bay contains the Senedd building (home to the Senedd, the Welsh Parliament) and the Wales Millennium Centre arts complex. Work continues at Cardiff Bay and in the centre, on projects such as Cardiff International Sports Village, BBC drama village, and a new business district.