one of the Channel Islands, in the English Channel, separated from the Normandy coast (Cap de la Hague) by the dangerously swift 10-mile (16-km) Race of Alderney. Swinge Race, on the west, separates it from the uninhabited Burhou, Ortac, and smaller islets, beyond which the notorious Casquets, a group of jagged rocks, carry a lighthouse. The nearest English coast is 55 miles (88 km) north.

The island is a tableland that is mostly above 200 feet (60 metres) and little dissected. Steep cliffs rise to 275 feet (83 metres) on the south and west coasts, while old cliffs rise behind raised beaches on the north and east. The two main inlets are Braye Harbour, protected by a 1,000-yard (914-metre) breakwater on the north, and Longy Bay (southeast), backed by a nearly filled lagoon.

The earliest known inhabitants were builders of megalithic tombs. The Bronze Age is well-represented, and the Romans appear to have built a small fort (the Nunnery) on the island. From the 11th century it was part of the Norman domain and was occupied by the French from 1338 to 1340. In 1559 it was leased to George Chamberlain and granted (1584) by letters patent to his brother John, who transferred it to the earl of Essex; his descendants held it until the English Civil War. From the Restoration until 1825, the government of Alderney was separated from that of Guernsey, being granted in 1660 to Edward de Carteret, who transferred it in 1661 to Sir George Carteret. Sir George's widow sold it to Edmund Andros of Guernsey (c. 1682), from whom it descended to the Le Mesurier family. Alderney is now in the Bailiwick of Guernsey but has its own local administration. Under the reformed constitution of 1949, the president and States of Alderney (10 members) are popularly elected; the Court of Alderney administers justice. During the 19th century, the island was heavily fortified by the British, who maintained a garrison there until 1930. Repatriation of the Alderney community, evacuated to England in 1940 prior to German occupation, was carried out after the war. The Alderney breed of dairy cattle was also evacuated, but none were returned, ending the native line. As a result, it was necessary to re-create the island's economy, based mainly on dairy farming and tourism. Most inhabitants live in the only town, St. Anne's, overlooking Braye Harbour; Newtown forms an appendage at a lower level. Communications are through Guernsey, to which Alderney is linked by air and shipping services. Area 3 square miles (8 square km). Pop. (2001) 2,294.