Ents are sentient beings 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.

Tolkien wrote almost nothing of the early history of the Ents. After the Dwarves were put to sleep by Eru to await the coming of the Elves, the Vala Aulë told his wife Yavanna, "the lover of all things that grow in the earth," of the Dwarves. She replied, "They will delve in the earth, and the things that grow and live upon the earth they will not heed. Many a tree shall feel the bite of their iron without pity." She went to Manwë and appealed to him to protect the trees, and they realized that Ents, too, were part of the Song of Creation. Yavanna then warned Aulë, "Now let thy children beware! For there shall walk a power in the forests whose wrath they will arouse at their peril." The Ents are called "the Shepherds of the Trees". Much later, when Beren and a force of Green Elves waylay the force of Dwarves returning from the sack of Doriath, the Dwarves are routed and scatter into the wood, where the Shepherds of the Trees ensure that none escape. Ents did not know how to speak until the Elves taught them. Treebeard said that the Elves "cured us of dumbness", calling that a great gift that could not be forgotten. At that time, much of Eriador was forested; Elrond stated that "a squirrel could go from tree to tree from what is now the Shire to Dunland west of Isengard."

The Entwives began to move farther away from the Ents because they liked to plant and control things, while the Ents preferred forests and liked to let things take their natural course. The Entwives moved away to what became the Brown Lands across the Great River Anduin, although the male Ents still visited them. The Entwives interacted with Men and taught them the art of agriculture. The gardens of the Entwives were destroyed by Sauron, and the Entwives disappeared. It was sung by the Elves that one day the Ents and Entwives would find each other. Treebeard indeed implored the Hobbits to send word to him if they had news of the Entwives.

Tolkien spent much time considering the fate of the Entwives, stating in Letters #144: "I think that in fact the Entwives have disappeared for good, being destroyed with their gardens in the War of the Last Alliance...some may have fled east, or even have become enslaved..."

After Aragorn is crowned king, he promised Treebeard that the Ents could prosper again and spread to new lands with the threat of Mordor gone, and renew their search for the Entwives. Treebeard lamented that forests may spread but the Ents would not, and he predicted that the few remaining Ents would remain in Fangorn forest and dwindle or become "treeish".

The Ents, angry at Saruman for cutting down their trees, convene an Entmoot. They decide to march on Saruman's fortress at Isengard - 'the last march of the Ents'. Led by Treebeard and accompanied by the hobbits Meriadoc Brandybuck and Peregrin Took, the Ents numbered about 50, plus an army of Huorns. They destroy Isengard, tearing down the wall around it: "If the Great Sea had risen in wrath and fallen on the hills with storm, it could have worked no greater ruin". Saruman is trapped in the tower of Orthanc.

The word "Ent" is from the Old English ent or eoten, meaning "giant". Tolkien borrowed the word from a phrase in the Anglo-Saxon poems The Ruin and Maxims II, orþanc enta geweorc ("cunning work of giants"), which describes Roman ruins.

In Sindarin, one of Tolkien's invented Elvish languages, the word for Ent is Onod (plural Enyd). The Sindarin word Onodrim means the Ents as a race.