Valinor (Quenya: Land of the Valar), the Blessed Realm, or the Undying Lands is a fictional location in J. R. R. Tolkien's legendarium, the home of the immortal Valar and Maiar on the continent of Aman, far to the west of Middle-earth; he used the name Aman mainly to mean Valinor. It includes Eldamar, the land of the Elves, who as immortals are permitted to live in Valinor.

The name "the Undying Lands" does not mean that the land itself causes mortals to live forever. Generally, only immortal beings are allowed to reside there. Exceptions are made for the surviving bearers of the One Ring: Bilbo and Frodo Baggins and Sam Gamgee, who dwell there for a time, and the dwarf Gimli.

Tolkien's myth of the attempt of Númenor to capture Aman has been likened to the biblical Tower of Babel and the ancient Greek Atlantis, and the resulting destruction in both cases. They note, too, that a mortal's stay in Valinor is only temporary, not conferring immortality, just as, in medieval Christian theology, the Earthly Paradise is only a preparation for the Celestial Paradise that is above.

Others have compared the account of the beautiful Elvish part of the Undying Lands to the place dreamed of in the Middle English poem Pearl, and stated that the closest literary equivalents of Tolkien's descriptions of these lands are the imrama Celtic tales such as those about Saint Brendan from the early Middle Ages. The Christian theme of good and light (from Valinor) opposing evil and dark (from Mordor) has also been discussed.

Valinor lies in Aman ("Unmarred"), a continent on the west of Belegaer, the ocean to the west of Middle-earth. Ekkaia, the encircling sea, surrounds both Aman and Middle-earth. Tolkien wrote that the name "Aman" was "chiefly used as the name of the land in which the Valar dwelt". The Pelóri mountains run along the east coast; their highest peak is Taniquetil. Tolkien created no detailed maps of Aman; those drawn by Karen Wynn Fonstad, based on Tolkien's rough sketch of Arda's landmasses and seas, show Valinor about 700 miles (1,100 km) wide, west to east (from the Great Sea to the Outer Sea), and about 3,000 miles (4,800 km) long north to south. The continent of Aman extends from the Arctic latitudes of the Helcaraxë to the subpolar southern region of Arda – about 7,000 miles (11,000 km).

Eldamar is "Elvenhome", the "coastal region of Aman, settled by the Elves", wrote Tolkien. Eldamar was the true Eldarin name of Aman. In The Hobbit it is named "Faerie". The land is well-wooded, as Finrod "walk[ed] with his father under the trees in Eldamar" and the Teleri Elves have timber to build their ships. The city of the Teleri, on the north shore of the Bay is Alqualondë, the Haven of the Swans, whose halls and mansions are made of pearl. The harbour is entered through a natural arch of rock, and the beaches are strewn with gems given by the Noldor Elves. In the bay is the island of Tol Eressëa.

Calacirya (Quenya: "Light Cleft", for the light of the Two Trees that streams through the pass into the world beyond) is the pass in the Pelóri mountains where the Elven city Tirion is set. It is close to the Girdle of Arda (the Equator). After the hiding of Valinor, this is the only gap through the mountains of Aman.

In the extreme north-east, beyond the Pelóri, is the Helcaraxë, a vast ice sheet that joins the two continents of Aman and Middle-earth before the War of Wrath. To prevent anyone from reaching the main part of Valinor's east coast by sea, the Valar create the Shadowy Seas, and within these seas they set a long chain of islands called the Enchanted Isles.