The wyvern (/ˈwaɪvərn/ WY-vərn), sometimes spelled wivern (/ˈwɪvərn/ WIV-ərn), is a type of mythical dragon with two legs, two wings, and often a pointed tail.

The wyvern in its various forms is important in heraldry, frequently appearing as a mascot of schools and athletic teams (chiefly in the United States, United Kingdom, and Canada). It is a popular creature in European literature, mythology, and folklore. Today, it is often used in fantasy literature and video games. The wyvern in heraldry and folklore is rarely fire-breathing, unlike other dragons.

According to the Oxford English Dictionary, the word is a development of Middle English wyver (attested fourteenth century), from Anglo-French wivre (compare French: vouivre and guivre), which originate from Latin: vīpera, meaning "viper", "adder", or "asp". This coincides with earlier Germanic tradition, where dragons are portrayed as large venomous serpents, and so often called "worms" (compare Old English: wyrm, Middle Low German: worm, Middle High German: wurm). The wyvern is thus directly related to the French vouivre and guivre, then by extension, also, the Central European lindworm.

The concluding "–n" had been added by the beginning of the 17th century, when John Guillim in 1610 describes the "wiverne" as a creature that "partake[s] of a Fowle in the Wings and Legs ... and doth resemble a Serpent in the Taile". John Gibbon in 1682 emphasises that it "hath but two Legs".

Conversely, medievalist William Sayers proposes a more complex origin for the term. He notes that the Anglo-French guivre and its Middle English derivative ceased to retain the original sense of "venomous snake" after the Latin term was re-introduced into medieval Latin, freeing them up to take an alternative meaning. Adducing another meaning of wiver (this time Old English) and guivre, "light javelin", and noting partial resemblances between the size and shape of javelins and snakes, plus the later medieval era's increasing use of heavy armor and decreasing use of light javelins, he proposes that the concepts of "venomous snake" and "light javelin" were melded to produce a new term for a previously unimagined concept of flying snake, a kind of dragon.

The concept of winged snakes as mythological creatures appears across numerous ancient Mediterranean and Near Eastern cultures, representing a widespread archetypal form that would later influence the development of the wyvern in European tradition. The Egyptian goddess Wadjet, depicted as a winged cobra or uraeus, exemplifies this tradition and served as a protective deity of Lower Egypt from the Predynastic period onwards. Similar winged serpentine creatures appear in Mesopotamian iconography, particularly in Neo-Assyrian palace reliefs from the 9th-7th centuries BCE, where they function as apotropaic guardians.

The earliest Greek literary reference to creatures explicitly described as "winged serpents" and "winged dragons" (πτερωτῶν ὀφίων and πτηνοὶ δράκοντες) appears in Herodotus' Histories where they come from Arabia to Egypt in spring but are stopped and killed by ibises (sacred Egyptian birds) waiting for them at the pass. Similarly, Euripides' Medea (431 BCE), where they are identified as the chariot steeds of Helios that transport Medea from Corinth. This motif was subsequently adopted by Roman authors, with Ovid's Metamorphoses (8 CE) providing an expanded description of these serpentine creatures possessing both wings and fiery breath. The conflation of serpentine and draconic features in classical literature established a precedent for the morphological ambiguity that would characterize medieval depictions of such creatures.

In medieval British heraldry, the earliest documented use of "wyver" appears in The Great, Parliamentary, or Banneret's Roll of 1312. The term derives from the Anglo-Norman wivre and Old French guivre "poisonous snake", both ultimately descended from the Latin vipera (viper), indicating the creature's fundamentally serpentine nature. Throughout the 14th and 15th centuries, heraldic texts demonstrate considerable terminological fluidity, with "dragon," "wyrm," and "wyver" often used interchangeably for two-legged winged serpents. The taxonomic distinction between four-legged dragons and two-legged wyverns emerged gradually during the late medieval period, becoming codified in English heraldry during the 16th century. This distinction was further elaborated in subsequent heraldic manuals, including Gerard Legh's The Accedens of Armory (1562) and John Guillim's influential Display of Heraldrie (1610), which established the iconographic conventions that would persist in British heraldry.