Dragons are legendary creatures, typically with serpentine or otherwise reptilian traits, that feature in the myths of many cultures.

The two most familiar interpretations of dragons are European dragons, derived from various European folk traditions and ultimately related to Greek and Middle Eastern mythologies, and the unrelated Chinese dragon. The English word "dragon" derives from Greek δράκων (drákōn), "dragon, serpent of huge size, water-snake", which probably comes from the verb δρακεῖν (drakeîn) "to see clearly".

Dragons are usually shown in modern times with a body like a huge lizard, or a snake with two pairs of lizard-type legs, and able to emit fire from their mouths. The European dragon has bat-type wings growing from its back. A dragon-like creature with no front legs is known as a wyvern. Following discovery of how pterosaurs walked on the ground, some dragons have been portrayed without front legs and using the wings as front legs pterosaur-fashion when on the ground.

Although dragons occur in many legends around the world, different cultures have varying stories about monsters that have been grouped together under the dragon label. Some dragons are said to breathe fire or to be poisonous. They are commonly portrayed as serpentine or reptilian, hatching from eggs and possessing typically scaly or feathered bodies. They are sometimes portrayed as having especially large eyes or watching treasure very diligently, a feature that is the origin of the word dragon (Greek drakeîn meaning "to see clearly"). Some myths portray them with a row of dorsal spines. European dragons are more often winged, while Chinese dragons resemble large snakes. Dragons can have a variable number of legs: none, two, four, or more when it comes to early European literature.

Dragons are often held to have major spiritual significance in various religions and cultures around the world. In many Asian cultures dragons were, and in some cultures still are, revered as representative of the primal forces of nature, religion and the universe. They are associated with wisdom—often said to be wiser than humans—and longevity. They are commonly said to possess some form of magic or other supernatural power, and are often associated with wells, rain, and rivers. In some cultures, they are also said to be capable of human speech. In some traditions dragons are said to have taught humans to talk.

The term dragoon, for infantry that moved around on horseback yet still fought as foot soldiers, is derived from their early firearm, the "dragon", a wide-bore musket that spat flame when it fired, and was thus named for the mythical creature.

The word dragon derives from Greek δρακων, via Latin draco. It is attested in Middle English from the 13th century, in the context of medieval bestiaries and legends.

The Greek and Latin term referred to any great serpent, not necessarily mythological, and this usage was also current in English up to the 18th century. Today the great komodo lizard Varanus komodoensis is also known in English as the Komodo dragon. The King James Bible uses the words "serpent", "dragon" and "Devil" in a fairly interchangeable manner.

The association of the serpent with a monstrous opponent overcome by a heroic deity has its roots in the mythology of the Ancient Near East, including Canaanite (Hebrew, Ugaritic), Hittite and Mesopotamian. The Chaoskampf motif entered Greek mythology and ultimately Christian mythology, although the serpent motif may already be part of prehistoric Indo-European mythology as well, based on comparative evidence of Indic and Germanic material.

The "European dragon" (and its Near Eastern and Indic cognates) myth has quite different characteristics and origins from those of the Chinese dragon.

Dinosaur and mammalian fossils were occasionally mistaken for the bones of dragons and other mythological creature; for example, a discovery in 300 BC in Wucheng, Sichuan, China, was labeled as such by Chang Qu. Adrienne Mayor has written on the subject of fossils as the inspiration for myths in her book The First Fossil Hunters, and in an entry in the Encyclopedia of Geology she wrote: "Fossil remains generated a variety of geomyths speculating on the creatures' identity and cause of their destruction. Many ancient cultures, from China and India to Greece, America, and Australia, told tales of dragons, monsters, and giant heroes to account for fossils of animals they had never seen alive." In Australia, stories of such creatures may have referred to the land crocodiles, Quinkana sp., a terrestrial crocodile which grew from 5 to possibly 7 metres in length, or the 4 tonne monitor lizard Varanus priscus (formerly Megalania prisca) a giant, carnivorous goanna that might have grown to as long as 7 metres, and weighed up to 1,940 kilograms, or rainbow serpents (possibly Wonambi naracoortensis) that were part of the extinct megafauna of that continent.

In the book An Instinct for Dragons anthropologist David E. Jones suggests a hypothesis that humans just like monkeys have inherited instinctive reactions to snakes, large cats and birds of prey. Dragons have features that are combinations of these three. Our instinctive fear for these three would explain why dragons with similar features occur in stories from independent cultures on all continents. Other authors have suggested that especially under the influence of drugs or in dreams, this instinct may give raise to fantasies about dragons, snakes, spiders, etc., which would explain why these symbols are popular in drug culture. The traditional mainstream explanation to the folklore dragons does however not rely on human instinct, but on the assumption that fossil remains of dinosaurs gave rise to similar speculations all over the world.