Andúnië was the home of the Lords of Andúnië descended from Valandil, the well-known and well-respected nobles of Númenor. The port city was were the Númenóreans received their Elven friends from Tol Eressëa bearing gifts of enrichment, in the time before the shadow fell over Númenor. During the time after the KingTar-Ancalimon, Andúnië became a haven of the Elf-friends (also known as The Faithful) who advocated a continued friendship with the elves and obedience to the Valar.
As the mistrust of the Faithful and the Valar grew, the residents of Andúnië would receive the Elves as guests only in secret. With the Shadow falling further upon Númenor and its people, Armenelos became much larger and more important than Andúnie. By the latter-half of the Second Age, many of the Faithful from Andúnië were so mistrusted by the King's Men that they were forcibly removed from the city, and made to live in Rómenna.
Amandil, the last of the Lords of Andunie through his surviving elder son Elendil became the ancestor of the Kings of the Dúnedain who settled in Middle-earth. The city was destroyed when Númenor was destroyed.