Noar Hill is a 63-hectare (160-acre) biological Site of Special Scientific Interest south of Selborne in Hampshire. It is a Nature Conservation Review site, Grade 2, and part of East Hampshire Hangers Special Area of Conservation. An area of 20 hectares (49 acres) is a nature reserve managed by the Hampshire and Isle of Wight Wildlife Trust.It forms one of the westerly outposts of the chalk hills called the South Downs, and rises to a maximum height of about 210 metres above sea-level. The western and northern flanks slope fairly gently, but the eastern and southern flanks in places reach a gradient exceeding 60%.
Gilbert White, in his Natural History of Selborne, says of Noar Hill:
At each end of the village [Selborne], which runs from south-east to north-west, arises a small rivulet: that at the north-west end frequently fails: but the other is a fine perennial spring little influenced by drought or wet seasons, called Well-head. This breaks out of some high grounds adjoining to Nore Hill, a noble chalk promontory, remarkable for sending forth two streams into two different seas. The one to the south becomes a branch of the Arun, running to Arundel, and so falling into the British channel: the other to the north.
The western flanks and much of the summit are given over to arable fields. A smaller part of the summit, 20 hectares (about 49 acres) known as High Common, is covered with downland grasses and scrub. The northern, eastern and southern flanks are covered by deciduous woodland dominated by beech. Such beechwoods on steep hills in East Hampshire are termed "hangers".
High Common is the site of mediaeval chalk-workings – chalk was dug out and spread on nearby fields as fertilizer. The excavations have left an irregular network of pits and hollows of varying size, depth, and steepness. Because the ground is so uneven, High Common remained unploughed for centuries and was only used for grazing. It retains the ancient chalk downland flora which elsewhere has largely been lost.