The greater part of Alderney is a level table-land, more or less cultivated. The land continues flat to the edge of the south-eastern and southern cliffs, which present a magnificent succession of broken and perpendicular walls of rock. Towards the north-west, north, and east, the coast is less rocky, and is indented by several bays of tame and naked aspect, of which those of Crabby, Braye, and Longy are the most noticeable. Sandstone, granite, and porphyry are the chief geological formations. From the importance of the island in a military sense, it has been fortified by a chain of defensive works, extending round the northern coast from the Clanque Fort on the west to Fort Essex on the east. The cliffs of the southern shore form a very strong natural bulwark. An extensive granite breakwater has been constructed, protecting the bay of Braye towards the west, intended to form an additional defence, and to convert the bay into a secure harbour of refuge. The works have cost upwards of a million and a quarter sterling; but the new harbour is not much resorted to, and the value of the breakwater as a means of defence has been questioned. Fort Touraille stands on the eastern side of the new harbour, and is a strong fortification, mounting 50 heavy guns, with bomb-proof barracks and powder magazine.

The population of Alderney has increased rapidly of recent years, on account of the extensive public works. In 1841 it was only 1030, in 1871 it was 2738. The inhabitants are Protestants, and Alderney forms part of the diocese of Winchester. Though a French patois lingers in the island, English is generally spoken and universally understood. The climate is healthy, and there is abundance of good water. Corn is grown, but much of the sandy soil is in grass, affording excellent pasture to the diminutive but pretty cows for which Alderney is famous. The only exports are cattle and early potatoes. St Anne’s, the town of the island, is situated at some distance from the beach, overlooking the new harbour. It is plainly built, but has a fine new church in the early English style, erected as a memorial of the family of Le Mesurier, long the hereditary governors of the island. The only other architectural feature worthy of notice is a Gothic arch built as a memorial of the late Prince Albert of England.

Alderney seems to have been known to the Romans as Riduna, and Roman as well as Celtic remains have been discovered. It is subject to the British crown, and is a dependency of Guernsey. For its history and relation to English legislation, see the article on the Channel Islands. The internal government is vested in a judge appointed by the crown, and six jurats, chosen for life by the people; and these, with twelve douzainiers, who are popular representatives, but have not the power of voting, form the legislature. Justice is administered by the same judge jurats, and several other officers. In civil cases an appeal may be taken to the royal court of Guernsey, while all criminal cases are referred to Guernsey for decision. Two companies of infantry and a battery of artillery compose the local militia.

Off the western coast of Alderney there are many uninhabited rocky islands; and six miles to the westward lie the Casquets, a group of rocks extremely dangerous to ships coming up the English Channel. On these rocks there are three lighthouses, with revolving lights 112 feet above the water.