Númenor is the fictional island kingdom founded by Men descended from the Edain in J.R.R. Tolkien’s legendarium.
The Valar raised Númenor from the sea at the beginning of the Second Age as a reward for the Edain who had aided the Elves during the wars of the First Age. Its people, the Númenóreans, received longer lifespans than other Men and became a powerful maritime civilization.
Númenor’s history eventually turns tragic. Its rulers grow increasingly resentful of mortality and suspicious of the Ban of the Valar, which forbids them from sailing to the Undying Lands. Under Sauron’s influence, King Ar-Pharazôn attacks Aman, and the island is destroyed in a cataclysm.
Survivors establish the kingdoms of Gondor and Arnor in Middle-earth. Númenor is therefore also called Westernesse in some Tolkien texts, a name that can cause confusion with the island’s principal name.