In J. R. R. Tolkien's Middle-earth writings, the Dúnedain (Sindarin pronunciation: [ˈduːnɛˌdaɪn]; sing. Dúnadan; lit. 'Man of the West') were a race of Men, also known as the Númenóreans or Men of Westernesse (translated from the Sindarin term). Those who survived the sinking of their island kingdom and came to Middle-earth, led by Elendil and his sons, Isildur and Anárion, settled in Arnor and Gondor.

After the Downfall of Númenor, the name Dúnedain was reserved to Númenóreans who were friendly to the Elves: hostile survivors of the Downfall were called Black Númenóreans.

The Rangers were two secretive, independent groups of Dúnedain of the North (Arnor) and South (Ithilien, in Gondor) in the Third Age. Like their Númenórean ancestors, they had qualities like those of the Elves, with keen senses and the ability to understand the language of birds and beasts. They were trackers and hardy warriors who defended their respective areas from evil forces.

The Dúnedain were descended from the Edain, the Elf-friends: the few tribes of Men of the First Age who sided with the Noldorin Elves in Beleriand. The original leader of the Edain was Bëor the Old, a vassal of the Elf lord Finrod. His people settled in Eldar lands. At the beginning of the Second Age, the Valar gave the Edain Númenor to live on. Númenor was an island-continent located far to the west of Middle-earth, and hence these Edain came to be called Dúnedain: Edain of the West. Their first King was Lord Elros, a half-Elf, and also a descendant of Bëor.

These first Dúnedain are the Númenóreans. They became a great civilization, and began maritime pursuits for exploration, trade and power. Some returned to Middle-earth, creating fortress-cities along its western coasts, dominating the lesser men of these areas. In time the Númenóreans split into two rival factions: the Faithful, remaining loyal to the Valar and Elves, and the King's Men, who were eventually seduced by the Dark Lord, Sauron.

Ultimately Númenor was drowned in a great cataclysm, but a remnant of the Faithful escaped in nine ships. Led by Elendil, they established the Dúnedain kingdoms of Arnor and Gondor in Middle-earth. There is a suggestion, voiced by Faramir, son of the Steward of Gondor, that these descendants of Númenóreans are higher than other Men; but his speech on the matter has been described as "arrogant" and as such not necessarily to be taken literally.

Sauron's spirit also escaped, and fled back to Middle-earth, where he again raised mighty armies to challenge Gondor and Arnor. With the aid of Gil-galad and the Elves, Sauron was defeated, and the Third Age began. Sauron vanished into the East for many centuries, and Gondor and Arnor prospered. As Sauron re-formed and gathered strength, a series of deadly plagues came from the East. These struck harder in the North than the South, causing a population decline in Arnor. Arnor fractured into three kingdoms. The chief of the Nine Ringwraiths, the Witch-king of Angmar, assaulted and destroyed the divided Northern Dúnedain kingdoms from his mountain stronghold of Carn Dûm. After their fall, a remnant of the northern Dúnedain became the Rangers of the North, doing what they could to keep the peace in the near-empty lands of their Fathers. The surviving Dúnedain of Arnor retreated to the Angle south of Rivendell, while smaller populations settled in far western Eriador. The fragmentation of the kingdoms has been compared to that of the early Frankish kingdoms.

Over the centuries, many southern Dúnedain of Gondor intermarried with other Men. Their lifespan became shorter with each generation. Eventually, even the Kings of Gondor married non-Dúnedain women occasionally. Only in regions such as Dol Amroth did their bloodline remain pure. In the Fourth Age, the Dúnedain of Gondor and Arnor were reunited under King Aragorn II Elessar (the Dúnadan), a direct descendant of Elros and Elendil. He married Arwen, reintroducing Elf-blood into his family line. In addition to the Faithful, Men in the South manned Númenórean garrisons at places like Umbar. Many of these folk were turned toward evil by Sauron's teachings, and became known as the Black Númenóreans.