Danebury is an Iron Age hillfort in Hampshire, England, about 19 kilometres (12 mi) north-west of Winchester (grid reference SU323376). The site, covering 5 hectares (12 acres), was excavated by Barry Cunliffe in the 1970s. Danebury is considered a type site for hillforts, and was important in developing the understanding of hillforts, as very few others have been so intensively excavated.

Built in the 6th century BC, the fort was used for almost 500 years, during a period when the number of hillforts in Wessex greatly increased. Danebury was remodelled several times, making it more complex and resulting in it becoming a "developed" hillfort. It is a Scheduled Monument and a Local Nature Reserve called Danebury Hillfort. The Scheduled Monument is surrounded by a Site of Special Scientific Interest, designated as Danebury Hill.

Until the 19th century very little was known about hillforts, as none had been excavated and their original purpose had been long forgotten. In the medieval period, their construction was attributed variously to iconic figures such as King Arthur, King Alfred, the Danes, Julius Caesar, and even giants. By the 18th century, it was widely thought that hillforts were Roman in origin.

Interest in hillforts was roused by the investigation of a hillfort at Worlebury Hill in the early-19th century. The first excavation at Danebury was carried out in November 1859, under antiquarian Augustus Wollaston Franks. His workers cleared out an Iron Age pit that was 2 metres (7 ft) deep and 1.5 m (5 ft) in diameter, although they were not able to ascertain its purpose.

The first widespread investigation of hillforts was carried out in the second half of the 19th century under Augustus Pitt-Rivers. Pitt-Rivers' work on the hillforts of Sussex led him to the conclusion that most hillforts were built in the Iron Age, and it paved the way for future work on hillforts. In the 1920s and 1930s, there was "hillfort mania" in British archaeology; by 1940, about 80 had been archaeologically excavated.

In the late 1960s, Barry Cunliffe decided to examine a single hillfort and its surrounding territory in an attempt to shed light on Iron Age society, its politics, and population. With the permission of the site's owner, Hampshire County Council, archaeological excavations began in 1969 and continued until 1988. Over the twenty seasons archaeologists spent examining the site, they looked at the defences and the gateway, and excavated 57% of the interior, where the remains of wattle and timber houses were discovered. It was the lengthiest investigation of any hillfort in western Europe.

A further non-invasive survey was carried out in 1997, as part of the Wessex Hillforts Project, using a magnetometer.

There is no historical record of events in Iron Age Britain, so archaeological investigation is the only way to reconstruct the history of Danebury and other forts. It is impossible to state with certainty every significant event in the hillfort’s history, but where an event leaves an archaeologically identifiable trace, a general chronology can be established, although dates are much less easy to establish. The hillfort was occupied from the mid-6th century BC until around 100 BC, and the defences were remodelled numerous times.