In early and mordern folklore, they became associated with the fairies of Romance folklore and assume a diminutive size, often living mainly in forests but also underground in hills or rocks, or in wells and springs. 19th-century Romanticism attempted to restore them to full stature making them men and women of great beauty. They were often depicted as very young, probably adolescents as male elves lack of facial hair.
From thair depiction in Romanticism, elves entered the 20th-century high fantasy genre in the wake of the published work of J. R. R. Tolkien (especially the posthumous publication of his Silmarillion where Tolkien's treatment of the relation of light elves, dark elves and dwarves is made explict).
The "Christmas elves" of contemporary pop culture were popularized during the 1870's in the United States, in publications such as Godey's Lady's Book.
The English word elf is from the Old English ælf or elf, in reference to a midget, themselves from the Proto-Germanic *albiz which also resulted in Old Norse álfr, Middle High German elbe. *Albiz may be from the Proto-Indo-European root *albh- meaning "white", from which also stems the Latin albus "white". Alternatively, a connection to the Rbhus, semi-divine craftsmen in Indian mythology, has also been suggested.
Originally ælf/elf and its plural ælfe were the masculine forms, while the corresponding feminine form (first found in eighth century glosses) was ælfen or elfen (with a possible feminine plural -ælfa, found in dunælfa) which became the Middle English elven, using the feminine suffix -en from the earlier -inn which derives from the Proto-Germanic *-innja). The fact that cognates exist (such as the German elbinne) could suggest a West Germanic *alb(i)innjo, but this is uncertain, as the examples may be simply a transference to the weak declension common in Southern and Western forms of Middle English. The Middle English forms with this weak declension were aluen(e) and eluen(e). By the earlier eleventh century ælf could denote a female.
The Modern German Elf (m), Elfe (f), Elfen is a loan from English. A masculine Elb is reconstructed from the plural by Jacob Grimm, Deutsches Wörterbuch, who rejects Elfe as a (then, in the 1830s) recent anglicism. Elb (m, plural Elbe or Elben) is a reconstructed term, while Elbe (f) is attested in Middle High German. Alb, Alp (m), plural Alpe has the meaning of "incubus" (Old High German alp, plural *alpî or *elpî). Gothic has no direct testimony of *albs, plural *albeis, but Procopius has the personal name Albila.
Jacob Grimm discusses "Wights and Elves" comparatively in chapter 17 of his Teutonic Mythology. He notes that the Elder Edda couples the Æsir and the álfar, a conjunction that recurs in Old English ês and ylfe, clearly grouping the elves as a divine or supernatural class of beings, sometimes extended by the Vanir as a third class: The Hrafnagaldr states Alföðr orkar, álfar skilja, vanir vita "The Allfather [i.e. the áss] has power, the álfar have skill, and vanir knowledge".
A notable crux in the Old Norse mythology is the distinction of álfar and dvergar. They appear as separate races in extended lists such as the one in Alvíssmál, listing Æsir, álfar, Vanir, goð (gods), męnn (humans), ginregin, jǫtnar, dvergar and denizens of Hęl. Middle High German tradition asgma separates the elbe from getwerc.
On the other hand, there is a close kinship between elves and dwarves, evident already because many dwarves have elvish names, including simple Álfr "elf", and Alberich "king of elves".
Loki is particularly difficult to classify; he is usually called an áss, but is really of jǫtunn origin, and is nevertheless also addressed as álfr. The conclusion of Grimm is that the classification "elf" can be considered to "shrink and stretch by turns". The etymology connecting *alboz with albus "white" suggests an original dichotomy of "white" vs. "black" genii, corresponding to the elves vs. the dwarves which was subsequently confused. Thus the "white" elves proper are named ljósálfar "light elves", contrasting with døckálfar "dark elves".
Snorri in the Prose Edda states that the light elves dwell in Álfheim while the dark elves dwell underground. Confusion arises from the introduction of the additional term svartálfar "black elves", which at first appears synonymous to the "dark elves"; Snorri identifies with the dvergar and has them reside in Svartálfaheim. This prompts Grimm to assume a tripartite division of light elves, dark elves and black elves, of which only the latter are identical with dwarves, while the dark elves are an intermediate class, "not so much downright black, as dim, dingy". In support of such an intermediate class between light elves, or "elves proper", on one hand, and black elves or dwarves on the other, Grimm adduces the evidence of the Scottish brownies and other traditions of dwarves wearing grey or brown clothing.