Ceredigion (Welsh pronunciation: [kɛrɛˈdɪɡjɔn]) is a county and former kingdom in mid-west Wales. As Cardiganshire (Welsh: Sir Aberteifi), it was created in 1282, and was reconstituted as a county under that name in 1996, reverting to Ceredigion a day later. In extent the current county is more or less identical to the historic county.

In pre-Roman, and possibly Roman times, a part of southern Ceredigion was in the territory of the Demetae and possibly part of that of the Ordovices. According to Nennius, a 10th-century Welsh chronicler, Ceredig, son of the Welsh invader Cunedda, settled in the area in the 5th century. It remained a kingdom ruled by his descendants until it expanded and changed its name, first to Seisyllwg in the late 7th century and, after the union of Seisyllwg with the Kingdom of Dyfed, it was incorporated into Deheubarth in the mid 10th century.

In 1282, Edward I of England conquered the principality of Wales and divided the area into counties. The name Cardigan was an Anglicisation of the name for the historic kingdom of Ceredigion. One of thirteen traditional counties in Wales, Cardiganshire was also a vice-county. Cardiganshire was split into the five hundreds (administrative area) of Genau'r-Glyn, Ilar, Moyddyn, Penarth and Troedyraur. The area of the county became a district of Wales under the name Ceredigion in 1974 under the Local Government Act 1972 and, since 1996, has formed the county of Ceredigion.