Plymouth ( PLIH-məth) is a port city and unitary authority in Devon, South West England. It is located on Devon's south coast between the rivers Plym and Tamar, about 36 miles (58 km) southwest of Exeter and 193 miles (311 km) southwest of London. It is the most populous city in Devon.

Plymouth's history extends back to the Bronze Age, evolving from a trading post at Mount Batten into the thriving market town of Sutton, which was formally re-named as Plymouth in 1439 when it was made a borough. The settlement has played a significant role in English history, notably in 1588 when an English fleet based here defeated the Spanish Armada, and in 1620 as the departure point for the Pilgrim Fathers to the New World. During the English Civil War, the town was held by the Parliamentarians and was besieged between 1642 and 1646. In 1690 a dockyard was established on the River Tamar for the Royal Navy and Plymouth grew as a commercial shipping port throughout the Industrial Revolution.

After absorbing nearby settlements in 1914, the borough was awarded city status in 1928. During World War II, Plymouth suffered extensive damage in the Plymouth Blitz, leading to post-war rebuilding that significantly shaped its modern appearance. A further expansion of its boundaries in 1967 contributed to its current status as the 30th-most populous built-up area in the UK and the second-largest city in the South West after Bristol, with a population in 2022 of 266,862.

Plymouth's economy, historically rooted in shipbuilding and seafaring, has transitioned towards a service-based economy since the 1990s. It maintains strong maritime connections, hosting HMNB Devonport, the largest operational naval base in Western Europe, and offering ferry links to Brittany and Spain. The city is also home to the University of Plymouth, reflecting its educational and cultural significance. Today, the city is governed locally by Plymouth City Council and is represented nationally by three Members of Parliament.