An Area of Outstanding Natural Beauty (AONB) is an area of countryside considered to have significant landscape value in England, Wales or Northern Ireland, that has been specially designated by Natural England on behalf of the United Kingdom government; the Countryside Council for Wales on behalf of the Welsh Government; or the Northern Ireland Environment Agency on behalf of the Northern Ireland Executive.

The primary purpose of the AONB designation is to conserve and enhance the natural beauty of the landscape, with two secondary aims: meeting the need for quiet enjoyment of the countryside and having regard for the interests of those who live and work there. To achieve these aims, AONBs rely on planning controls and practical countryside management.

As they have the same landscape quality, AONBs may be compared to the national parks of England and Wales. AONBs are created under the same legislation as the national parks, the National Parks and Access to the Countryside Act 1949. Unlike AONBs, national parks have their own authorities, have special legal powers to prevent unsympathetic development, and are well known to many inhabitants of England, Wales and Northern Ireland. By contrast, there are very limited statutory duties imposed on local authorities within an AONB and there is evidence to indicate many residents in such areas may be unaware of the status. However, further regulation and protection of AONBs was added by the Countryside and Rights of Way Act 2000, and the Government has recently stated that AONBs and national parks have equal status when it comes to planning consent and other sensitive issues.