Tallinn is the capital and largest city of Estonia. It occupies an area of 159.2 km2 (61.5 sq mi) with a population of 412,341. It is situated on the northern coast of the country, on the banks of the Gulf of Finland, 80 km (50 mi) south of Helsinki, west of Saint Petersburg.

In 1154 a town called Qlwn or Qalaven (possible derivations of Kalevan or Kolyvan) was put on the world map of the Almoravid by cartographer Muhammad al-Idrisi who described it as a small town like a large castle among the towns of Astlanda. It has been suggested that the Quwri in Astlanda may have denoted the predecessor town of today's Tallinn.

The earliest names of Tallinn include Kolyvan (Russian: Колывань) known from East Slavic chronicles, the name possibly deriving from the Estonian mythical hero Kalev.

Up to the 13th century the Scandinavians and Henry of Livonia in his chronicle called the town Lindanisa: Lyndanisse in Danish, Lindanäs in Swedish, also mentioned as Ledenets in Old East Slavic. According to some theories the name derived from mythical Linda, the wife of Kalev and the mother of Kalevipoeg. who in an Estonian legend carried rocks to her husband's grave that formed the Toompea hill. It has been also suggested that in the context the meaning of linda in the archaic Estonian language, that is similar to lidna in Votic, had the same meaning as linna or linn later on meaning a castle or town in English. According to the suggestion nisa would have had the same meaning as niemi (meaning peninsula in English) in an old Finnish form of the name Kesoniemi.

Other than Kesoniemi known ancient historical names of Tallinn in Finnish include Rääveli. The Icelandic Njálssaga mentions Tallinn and calls it Rafala, which is a variant of the name Raphael. The incident may have happened around year 1000.

After the Danish conquest in 1219 the town became known in the German, Swedish and Danish languages as Reval (Latin: Revalia). The name originated from (Latin) Revelia (Estonian) Revala or Rävala, the adjacent ancient name of the surrounding Estonian county.

The origin of the name "Tallinn(a)" is certain to be Estonian, although the original meaning of the name is debated. It is usually thought to be derived from "Taani-linn(a)" (meaning "Danish-castle/town"; Latin: Castrum Danorum) after the Danes built the castle in place of the Estonian stronghold at Lindanisse. However, it could also have come from "tali-linna" ("winter-castle/town"), or "talu-linna" ("house/farmstead-castle/town"). The element -linna, like Germanic -burg and Slavic -grad / -gorod, originally meant "fortress" but is used as a suffix in the formation of town names.

The previously used official German name About this sound Reval (help·info) (Russian: Ревель) was replaced after Estonia became independent in 1918–1920. At first both forms Tallinna and Tallinn were used. The United States Board on Geographic Names adopted the form Tallinn between June 1923 and June 1927. The form Tallinna appearing in modern times in Estonian denotes the genitive case of the name, as in Tallinna Reisisadam (Port of Tallinn).

Other variations of modern spellings include Tallinna in Finnish and Та́ллин in Russian.

A form Tallin deriving from the Romanization of Russian spelling of the name Та́ллин was also used internationally during the era Estonia was annexed by the Soviet Union.