Númenor is the fictional island kingdom destroyed in J.R.R. Tolkien's mythology.
Númenor was an island realm granted to the Men who had aided the Elves during the First Age. Its people, the Númenóreans, were given long lives and great knowledge, and their civilization became one of the most powerful human cultures in Tolkien's world.
Over time, Númenórean leaders grew jealous of the immortality associated with the Elves and challenged the divine order of the world. Under Ar-Pharazôn, an invasion of Aman led to catastrophe. Eru Ilúvatar changed the shape of the world, and Númenor was overwhelmed and destroyed.
Survivors led by Elendil founded the realms of Arnor and Gondor in Middle-earth. The island's fall is sometimes confused with the destruction of Beleriand, which occurred much earlier during the First Age. Valinor, meanwhile, is a realm in Aman and was not the island kingdom destroyed in the same event.