In the fiction of J. R. R. Tolkien, the Long Winter was an extremely cold and long-lasting winter in Middle-earth.

The Long Winter began in November 2758 of the Third Age, and snow soon covered all of Eriador and Rhovanion all the way south to the Ered Nimrais. Sauron used the winter to his advantage, staging an attack on Gondor by the Corsairs of Umbar and fleets of the Haradrim, while at the same time Easterlings and Dunlendings backed by Corsairs attacked Rohan. King Helm Hammerhand was trapped in the Hornburg, where he was forced to make desperate raids on the Dunlendings led by Wulf in order to get food. Gondor was unable to send help as its coasts and east flank were under attack. In the north the people of Arnor also suffered greatly, dying of hunger.

The winter ended in March T.A. 2759, when great floods of smeltwater allowed Helm's nephew Fréaláf Hildeson to oust the Dunlendings from Rohan, and Gondor now could come for help so that Rohan was soon cleared.

See also the Fell Winter of 2911–2912.