The Chiltern Hills or the Chilterns are a chalk escarpment in southern England to the northwest of London, covering 660 square miles (1700 sq km) across Oxfordshire, Buckinghamshire, Hertfordshire and Bedfordshire and stretching 45 miles (72 km) from Goring-on-Thames in the southwest to Hitchin in the northeast. The hills are 12 miles (19 km) at their widest.
In 1964, 833 square kilometres - almost half of the Chiltern Hills - were designated by the Countryside Commissionas an Area of Outstanding Natural Beauty (AONB) under the powers established by the National Parks and Access to the Countryside Act 1949.