Alderney is the most northerly of the Channel Islands. It is part of the Bailwick of Guernsey a British crown dependency. It is 4.8 kilometres long and 2.4 kilometres wide. The area is 7.8 km2, making it the third-largest island of the Channel Islands. It is 16 km to the west of La Hague on the Normandy (French) peninsula.

The island has a population of only 2,600 people. The only parish on Alderney is the parish of St Anne, which covers the whole island. The Alderney coastline consists of sheer cliffs and stretches of sandy beach and dunes. The highest point on the island is the central plateau. This stands about 100 metres above sea level.

Alderney enjoys a temperate climate. Summers are usually warmer than elsewhere in the British Isles. Alderney and the surrounding smaller islands support a wide range of flora and fauna. However, trees are scarce, as many were cut down in the 17th century to fuel the lighthouses on Alderney.

Puffins on Burhou and Gannets on Les Étacs just off Alderney are a favourite of many visitors to the island. About a quarter of the hedgehogs found on the island are of the "white" or "blonde" variety, and do not carry fleas.

The island had its own breed of cattle, called the Alderney. Sadly the breed became extinct in 1944 during the German occupation.In August 2005, the west coast of Alderney and associated islands, including Burhou and Antac were designated as Ramsar Wetlands of international importance. The Alderney Wildlife Trust helps to manage the two nature reserves at Longis and Vau du Saou.