Tenby Castle (Welsh: Castell Dinbych-y-pysgod) is a fortification which stands on a headland separated by an isthmus from the town of Tenby, Pembrokeshire, Wales. The remaining stone structure dates from the 13th century but there are mentions of the castle from as early as 1153. It is a Grade II* listed building.
St Catherine's Fort, a Palmerston Fort, stands just offshore of the medieval castle.
The castle, which was sited on a rocky promontory, was founded by the Normans during their invasion of West Wales in the 12th century. A stone tower was built on the headland's highest point which was protected by a curtain wall. The walls had a gateway and several small towers on the landward side. A lesser sea wall surrounded the remainder of the site and the beach area to the west.
In 1153, the castle was captured and destroyed by Maredudd ap Gruffydd and Rhys ap Gruffydd, the future ruler of the south-western petty kingdom of Deheubarth in mid Wales. The castle was besieged again by the Welsh in 1187. Although Llywelyn ap Gruffudd sacked the town during his campaign to retake South Wales in 1260, the castle was not captured. In the late 13th century, the castle and the town had become part of the feudal lands of William de Valence, 1st Earl of Pembroke.
The French knight, who had been given the peerage for his military services for Henry III in the Second Barons' War, instigated the building of stone walls around the town. However, this diminished the defensive importance of Tenby Castle. By the end of the 13th century, the walls enclosing Tenby's old town were mostly completed. In 1328, a D-shaped barbican was built to defend the town's main gate. Additional D-shaped towers were also added to the northern and southern walls. Tenby castle was largely abandoned and in disrepair by the 1400s.