St Kilda  is a remote archipelago situated 35 nautical miles (65 km; 40 mi) west-northwest of North Uist in the North Atlantic Ocean. It contains the westernmost islands of the Outer Hebrides of Scotland. The largest island is Hirta, whose sea cliffs are the highest in the United Kingdom; three other islands (Dùn, Soay and Boreray) were also used for grazing and seabird hunting. The islands are administratively a part of the Comhairle nan Eilean Siar local authority area.

The origin of the name St Kilda is a matter of conjecture. The islands’ human heritage includes unique architectural features from the historic and prehistoric periods, although the earliest written records of island life date from the Late Middle Ages. The medieval village on Hirta was rebuilt in the 19th century, but illnesses brought by increased external contacts through tourism, and the upheaval of the First World War, contributed to the island’s evacuation in 1930. Permanent habitation on the islands possibly extends back two millennia, the population probably never exceeding 180; its peak was in the late 17th century. The population waxed and waned, eventually dropping to 36 in 1930,  when the remaining population was evacuated. Currently, the only year-round residents are military personnel; a variety of conservation workers, volunteers and scientists spend time there in the summer months. The entire archipelago is owned by the National Trust for Scotland.

A cleit is a stone storage hut or bothy unique to St Kilda; there are known to be 1,260 cleitean on Hirta and a further 170 on the other group islands. Two different early sheep types have survived on these remote islands: the Soay, a Neolithic type, and the Boreray, an Iron Age type. The islands are a breeding ground for many important seabird species including northern gannets, Atlantic puffins, and northern fulmars. The St Kilda wren and St Kilda field mouse are endemic subspecies.

It became one of Scotland’s six World Heritage Sites in 1986, and is one of the few in the world to hold joint status for both its natural and cultural qualities.

The name St Kilda, which is not used in Gaelic, is of obscure origin, as there is no saint by the name Kilda. It occurs for the first time in Thresoor der Zeevaert (“Treasure of Navigation”), a pilot book published by Lucas Waghenaer in 1592. A. B. Taylor suggests that it originated as a copying error for Skilda(r), a name that appears on Nicolas de Nicolay’s 1583 map of Scotland, which Waghenaer used as a source. On Nicolay’s map, the name denotes an island group closer to Lewis and Harris than St Kilda, possibly Haskeir,  Gasker or Haskeir Eagach. Taylor notes that the latter two groups could be compared to shields lying flat upon the water, and gives the Norse word skildir (meaning “shields”) as the etymon.

According to another theory, advanced by William J. Watson and others, the name derives from Tobar Childa, an important well on Hirta. Childa is in fact a descendant of kelda, the Norse word for a well, but it is possible that visitors to the island (who would have used the well to take on fresh water) mistook it as the name of a local saint. A number of other theories have been suggested in both the past and in modern times.

The origins of Hiort, and its anglicized form Hirta,which long pre-date St Kilda, are similarly obscure. Watson derives it from the Gaelic word (h)irt, meaning “death”, noting that although Alexander MacBain suggested “that the ancient Celts fancied this sunset isle to be the gate to their earthly paradise” the connection was more likely to be to the dangers of living on St Kilda, which “in the Hebrides is regarded as a penitentiary rather than a gate to paradise”. It has also been said to mean “the western land”, from the Gaelic (na) h-iartìre although this theory presents difficulties. It may not be Gaelic in origin at all, but rather Norse. Taylor derives it from the Norse word hirtir, meaning “stags”, on account of the islands’ “jagged outlines”. In support of this theory, he notes that Hirtir appears in the 13th-century Prestssaga Guðmundar Arasonar as a name for an island group in the Hebrides.

As with St Kilda, a number of other theories have been offered. All the names of and on the islands are discussed by Richard Coates.