Ents are giant humanoids in J. R. R. Tolkien's fantasy world of Middle-earth who closely resemble trees; their leader is Treebeard of Fangorn forest. Their name is derived from an Old English word for "giant".

The Ents appear in The Lord of the Rings as ancient shepherds of the forest and allies of the free peoples of Middle-earth during the War of the Ring. The Ent who figures most prominently in the book is Treebeard, who is called the oldest creature in Middle-earth. At that time, there are no young Ents (Entings) because the Entwives (female Ents) were lost. Akin to Ents are Huorns, whom Treebeard describes as a transitional form of trees which become animated or, conversely, as Ents who grow more "treelike" over time.

Tolkien stated that he was disappointed by Shakespeare's handling of the coming of "Great Birnam Wood to High Dunsinane hill"; he wanted a setting in which the trees would actually go to war. Commentators have seen this as wish-fulfilment, as he disliked the damage being done to the English countryside in his lifetime. Scholars have seen his tale of the Ents as a myth, mostly without analysing it. Corey Olsen interprets the song of the Ents and the Entwives as a myth that warns of the dangers of apathetically isolating oneself in nature, whereas the Ents' song "In the willow-meads of Tasarinan" is a lament.

Inspired by Tolkien and similar traditions, animated or anthropomorphic tree creatures appear in a variety of media and works of fantasy.

Treebeard, called by Gandalf the oldest living Ent and the oldest living thing that walks in Middle-earth, is described as being around 14 feet (4 m) tall, "Man-like, almost Troll-like", and clad in something that might have been tree-bark, with seven toes, a bushy, "almost twiggy" beard and deep penetrating eyes. Ents vary widely in personal traits (height, heft, colouring, even the number of toes), having come to resemble somewhat the specific types of trees that they shepherded. Quickbeam, for example, guarded rowan trees and bore some resemblance to rowans: tall and slender, smooth-skinned, with ruddy lips and grey-green hair. Some Ents, such as Treebeard, were like

beech-trees or oaks. But there were other kinds. Some recalled the chestnut: brown-skinned Ents with large splayfingered hands, and short thick legs. Some recalled the ash: tall straight grey Ents with many-fingered hands and long legs; some the fir (the tallest Ents), and others the birch, ... and the linden.

Ents are somewhat treelike, with extraordinarily tough skin; they can erode stone rapidly, but are vulnerable to fire and axe-strokes. They are patient and cautious, with a long sense of time; they considered a three-day deliberation "hasty".

Ents are tall and very strong, capable of tearing apart rock and stone when "roused". Tolkien describes them as tossing great slabs of stone about, and ripping down the walls of Isengard "like bread-crust". Treebeard boasted of their strength to Merry and Pippin; he said that Ents were much more powerful than Trolls, which Morgoth made in the First Age in mockery of Ents, as Orcs were of Elves.