Cardigan Castle (Welsh: Castell Aberteifi) is a castle overlooking the River Teifi in Cardigan, Ceredigion, Wales. It is a Grade I listed building. The castle dates from the late 11th-century, though was rebuilt in 1244. Castle Green House was built inside the castle walls in the early 1800s. After falling into disrepair the castle was restored in the early 2000s and opened to the public in 2015. It is owned by Ceredigion County Council and now includes a heritage centre and open-air concert facilities. The castle's gardens are listed on the Cadw/ICOMOS Register of Parks and Gardens of Special Historic Interest in Wales.

The first motte-and-bailey castle (ca.1093) was built a mile away from the present site, probably about the time of the founding of the town by Roger de Montgomery, a Norman baron.

In 1110, King Henry I of England took Cardigan from Prince Owain ap Cadwgan as a punishment, and gave the Lordship of Cardigan and the castle to Gilbert Fitz Richard. The forerunner of the present castle was built by Gilbert Lord of Clare after the former was destroyed.

The castle was handed down to Gilbert's son, Gilbert de Clare, 1st Earl of Pembroke in 1136. The same year, Owain Gwynedd led the defeat of the Norman rulers in the town of Cardigan at the Battle of Crug Mawr. The town was taken and burnt, though the castle was successfully defended by Normans commanded by Robert fitz Martin.^{[citation needed]}

The castle was later recaptured by the Normans, and was held for Earl Roger of Hertford. In 1166 it was captured by Rhys ap Gruffydd, who rebuilt it in stone in 1171. In 1176 the first recorded eisteddfod was held at the castle.

After Rhys's death in 1197 his sons, Maelgwn and Gruffydd, disputed their inheritance resulting in Maelgwn surrendering Gruffydd to the Normans and selling the castle to King John. The castle was later held for William Marshall.^{[citation needed]}

Llywelyn the Great captured it in 1215 and at the parliament held at Aberdyfi in 1216 made it over to the sons of Gruffydd ap Rhys of Deheubarth, but in 1223 William Marshall the Younger recaptured it. In 1231 the castle was again captured for Llywelyn by Rhys Gryg and his allies. Llywelyn held it until his death in 1240. On Llywelyn's death it fell back into Norman hands, and in 1244 Earl Gilbert of Pembroke rebuilt it with town walls for added protection. It is the remains of this building that still stands overlooking the river.

It was badly damaged during the English Civil War in Wales and until the 18th century it was only used as a prison.^{[citation needed]}