Peterborough (/ˈpiːtərbərə, -bʌrə/ ^ⓘ PEE-tər-bər-ə, -⁠burr-ə) is a cathedral city in the City of Peterborough district in the ceremonial county of Cambridgeshire, England. The city is 74 miles (119 km) north of London, on the River Nene. As of the 2021 census, Peterborough had a population of 192,178, while the population of the district was 215,673.

Human settlement in the area began before the Bronze Age, as can be seen at the Flag Fen archaeological site to the east of the city centre. There is evidence of Roman occupation. The Anglo-Saxon period saw the establishment of a monastery, Medeshamstede, which later became Peterborough Cathedral. In the 19th century, the population grew rapidly after the coming of the railway. The area became known for its brickworks and engineering. After the Second World War, industrial employment fell and growth was limited until Peterborough was designated a new town in the 1960s. The main economic sectors now are financial services and distribution.

The city was the administrative centre of the Soke of Peterborough in the historic county of Northamptonshire, until the Soke was abolished in 1965. From 1965 to 1974, it formed part of the short-lived county of Huntingdon and Peterborough and since then has been part of Cambridgeshire.

The cathedral city of Ely is 24 miles (39 km) east-southeast across the Fens and the university city of Cambridge is 30 miles (48 km) to the southeast. The local topography is flat, and in places, the land lies below sea level.

The original name of the town was Medeshamstede. The town's name changed to Burgh from the late tenth century, possibly after Abbot Kenulf had built a defensive wall around the abbey which was dedicated to Saint Peter; eventually this developed into the form Peterborough. In the 12th century, the town was also known as Gildenburgh, which is found in the Peterborough version of the Anglo-Saxon Chronicle (see Peterborough Chronicle below) and a history of the abbey by the monk Hugh Candidus. The town does not appear to have been a borough until at least the 12th century.

Peterborough and its surrounding areas around have been inhabited for thousands of years because it is where permanently drained land in The Fens is created by the River Nene. Remains of Iron Age settlement and what is thought to be religious activity can be seen at the Flag Fen archaeological site to the east of the city centre. The Romans established a fortified garrison town at Durobrivae on Ermine Street, five miles (8.0 km) to the west in Water Newton, around the middle of the 1st century AD. Durobrivae's earliest appearance among surviving records is in the Antonine Itinerary of the late 2nd century. There was also a large 1st century Roman fort at Longthorpe, designed to house half a legion, or about 3,000 soldiers; it may have been established as early as around AD 44–48. Peterborough was an important area of ceramic production in the Roman period, providing Nene Valley Ware that was traded as far away as Cornwall and the Antonine Wall, Caledonia.

Peterborough is shown by its original name Medeshamstede to have possibly been an Anglian settlement before AD 655, when Sexwulf founded a monastery on land granted to him for that purpose by Peada of Mercia, who converted to Christianity and was briefly ruler of the smaller Middle Angles sub-group. His brother Wulfhere murdered his own sons, similarly converted and then finished the monastery by way of atonement.

Hereward the Wake rampaged through the town in 1069 or 1070. Outraged, Abbot Turold erected a fort or castle, which, from his name, was called Mont Turold: this mound, or hill, is on the outside of the deanery garden, now called Tout Hill, although in 1848 Tot-hill or Toot Hill. The abbey church was rebuilt and greatly enlarged in the 12th century. The Peterborough Chronicle, a version of the Anglo-Saxon one, contains unique information about the history of England after the Norman conquest, written here by monks in the 12th century. This is the only known prose history in English between the conquest and the later 14th century. The burgesses received their first charter from "Abbot Robert" – probably Robert of Sutton (1262–1273). The place suffered materially in the war between King John and the confederate barons, many of whom took refuge in the monastery here and in Crowland Abbey, from which sanctuaries they were forced by the king's soldiers, who plundered the religious houses and carried off great treasures. The abbey church became one of Henry VIII's retained, more secular, cathedrals in 1541, having been assessed at the Dissolution as having revenue of £1,972.7s.0¾d per annum.