In the fiction of J. R. R. Tolkien, Dorthonion ("Land of Pines"), later Taur-nu-Fuin, was a highland region of the First Age, lying immediately to the north of Beleriand, and south of the plains of Ard-galen (later Anfauglith) that bordered Morgoth's stronghold of Thangorodrim.

Dorthonion was 60 leagues east to west. In the north it rose gradually from the plains, with great pine forests. The Ered Gorgoroth (Mountains of Terror) formed the southern boundary of Dorthonion, bending to the north on the east side to create the Pass of Aglon between Dorthonion and Hills of Himring. In the south and east of Dorthonian were the Echoriath (Encircling Mountains) in which was Gondolin. The upper reaches of the River Sirion passed between the western slopes of Dorthonion and the Ered Wethrin (Mountains of Shadow).

Dorthonion was originally ruled by Angrod and Aegnor, sons of Finarfin, but it was overrun by Morgoth in the Dagor Bragollach, after which it was known as Taur-nu-Fuin ("Forest under Night").

The north-eastern slopes of Dorthonion were known as Ladros, which was a fief given to Boromir of the House of Bëor. Here Barahir and later his son Beren dwelt in the wilderness.

Along with the other lands east of the Ered Luin, Taur-nu-Fuin was mostly destroyed in the War of Wrath at the end of the First Age. Its highest parts survived as the island Tol Fuin (Isle of Night), part of the Western Isles.