An elf (PL elves) is a type of humanoid supernatural being in Germanic mythology and folklore. Elves appear especially in North Germanic mythology, being mentioned in the Icelandic Poetic Edda and Snorri Sturluson's Prose Edda.

In medieval Germanic-speaking cultures, elves generally seem to have been thought of as beings with magical powers and supernatural beauty, ambivalent towards everyday people and capable of either helping or hindering them. However, the details of these beliefs have varied considerably over time and space and have flourished in both pre-Christian and Christian cultures.

Sometimes elves are, like dwarfs, associated with craftmanship. Wayland the Smith embodies this feature. He is known under many names, depending on the language in which the stories were distributed. The names include Völund in Old Norse, Wēland in Anglo-Saxon and Wieland in German. The story of Wayland is also to be found in the Prose Edda.

The word elf is found throughout the Germanic languages and seems originally to have meant 'white being'. However, reconstructing the early concept of an elf depends largely on texts written by Christians, in Old and Middle English, medieval German, and Old Norse. These associate elves variously with the gods of Norse mythology, with causing illness, with magic, and with beauty and seduction.

After the medieval period, the word elf tended to become less common throughout the Germanic languages, losing out to alternative native terms like Zwerg ('dwarf') in German and huldra ('hidden being') in North Germanic languages, and to loan-words like fairy (borrowed from French into most of the Germanic languages). Still, beliefs in elves persisted in the early modern period, particularly in Scotland and Scandinavia, where elves were thought of as magically powerful people living, usually invisibly, alongside everyday human communities. They continued to be associated with causing illnesses and with sexual threats. For example, several early modern ballads in the British Isles and Scandinavia, originating in the medieval period, describe elves attempting to seduce or abduct human characters.

With urbanisation and industrialisation in the nineteenth and twentieth centuries, beliefs in elves declined rapidly (though Iceland has some claim to continued popular belief in elves). However, elves started to be prominent in the literature and art of educated elites from the early modern period onwards. These literary elves were imagined as tiny, playful beings, with William Shakespeare's A Midsummer Night's Dream being a key development of this idea. In the eighteenth century, German Romantic writers were influenced by this notion of the elf and re-imported the English word elf into the German language.

From the Romantic idea of elves came the elves of popular culture that emerged in the nineteenth and twentieth centuries. The "Christmas elves" of contemporary popular culture are a relatively recent creation, popularized during the late nineteenth century in the United States. Elves entered the twentieth-century high fantasy genre in the wake of works published by authors such as J. R. R. Tolkien; these re-popularised the idea of elves as human-sized and humanlike beings. Elves remain a prominent feature of fantasy media today.