Windmill Hill is a Neolithic causewayed enclosure in the English county of Wiltshire, situated around 3 miles north of Avebury. It is the largest example of its type in the British Isles enclosing an area of 8.5 ha. The site was first occupied around 3800 BC although the only evidence is a series of pits apparently dug by an agrarian society using Hembury pottery.

During a later phase, c. 3300 BC, three concentric segmented ditches were placed around the hilltop site, the outermost with a diameter of 365 metres. The causeways interrupting the ditches vary in width from a handful of centimetres to up to 7m. Material from the ditches was piled up to create internal banks, the deepest ditches and largest banks are on the outer circuit.

The site was excavated in 1926 by Harold St George Gray whose work established it as the type-site for causewayed camps as they were then called.

Pottery from the bottom of the ditches was also the type style for the Windmill Hill culture. Later occupation layers contained early Peterborough ware then the later Mortlake and Fengate varieties. Large quantities of bone, both human and animal were also recovered from the ditch fill. The camp remained in use throughout the rest of the Neolithic with Grooved ware and Beaker potsherds having been found in later deposits. A Bronze Age bell barrow was later built between the inner and middle rings.