Areas of Outstanding Natural Beauty, protected countryside areas throughout Britain designated for their landscape and natural beauty. Areas of Outstanding Natural Beauty (AONBs) are designated by the Countryside Agency, in England, the Countryside Council for Wales, in Wales, and the Environment and Heritage Service, in Northern Ireland. In Scotland, the equivalent to an AONB is a National Scenic Area, designated by Scottish Natural Heritage, although they differ slightly from AONBs.

AONBs in England and Wales are established under the same legislation that created the National Parks—the National Parks and Access to the Countryside Act of 1949. The main difference between the two is that creating opportunities for recreation is not a specific purpose of the AONBs, although AONBs are required to meet the demands of recreation as far as this is consistent with the conservation of natural beauty and the needs of agriculture, forestry, and other users. Areas where the landscape is considered to be of value to the nation, but which lack opportunities for recreation, tend to be designated as AONBs. In designating an area as an AONB, the economic and social needs of the local communities are taken into account, as well as the need to safeguard agriculture, forestry, and other rural industries.

Although AONBs usually have funding to help promote good management and encourage sustainable forms of social and economic development, which in turn can protect and promote the environment, they do not have legal, statutory protection. Instead, AONBs are managed by local authorities who are expected to take the special character of the landscape into account when forming policy and controlling development.

There are currently 41 AONBs in England and Wales, covering about 14 per cent of the countryside—36 in England, 4 in Wales, and the Wye Valley, which is in both. They range in size from the Scilly Isles, which is the smallest at 16 sq km (6 sq mi), to the Cotswolds, which is the largest at 2,038 sq km (787 sq mi). Northern Ireland has 9 designated AONBs, and there are 40 National Scenic Areas in Scotland.