The Elvish languages of Middle-earth, constructed by J. R. R. Tolkien, include Quenya and Sindarin. These were the various languages spoken by the Elves of Middle-earth as they developed as a society throughout the Ages. In his pursuit for realism and in his love of language, Tolkien was especially fascinated with the development and evolution of language through time. Tolkien created two almost fully developed languages and a dozen more in various beginning stages as he studied and reproduced the way that language adapts and morphs. A philologist by profession, he spent much time on his constructed languages. In the collection of letters he had written, posthumously published by his son, Christopher Tolkien, he stated that he began stories set within this secondary world, the realm of Middle-earth, not with the characters or narrative as one would assume, but with a created set of languages. The stories and characters serve as conduits to make those languages come to life. Inventing language was always a crucial piece to Tolkien's mythology and world building. As Tolkien stated:

The invention of languages is the foundation. The 'stories' were made rather to provide a world for the languages than the reverse. To me a name comes first and the story follows.

Tolkien created scripts for his Elvish languages, of which the best known are Sarati, Tengwar, and Cirth.

J. R. R. Tolkien began to construct his first Elvin tongue c. 1910–1911 while he was at the King Edward's School, Birmingham and which he later named Quenya (c. 1915). At that time, Tolkien was already familiar with Latin, Greek, Italian, Spanish, and three ancient Germanic languages: Gothic, Old Norse, and Old English. He had invented several cryptographic codes such as Animalic, and two or three constructed languages including Naffarin. He then discovered Finnish, which he described many years later as "like discovering a complete wine-cellar filled with bottles of an amazing wine of a kind and flavour never tasted before. It quite intoxicated me."

The ingredients in Quenya are various, but worked out into a self-consistent character not precisely like any language that I know. Finnish, which I came across when I first begun to construct a 'mythology' was a dominant influence, but that has been much reduced [now in late Quenya]. It survives in some features: such as the absence of any consonant combinations initially, the absence of the voiced stops b, d, g (except in mb, nd, ng, ld, rd, which are favoured) and the fondness for the ending -inen, -ainen, -oinen, also in some points of grammar, such as the inflexional endings -sse (rest at or in), -nna (movement to, towards), and -llo (movement from); the personal possessives are also expressed by suffixes; there is no gender.

Tolkien with his Quenya pursued a double aesthetic goal: "classical and inflected". This urge was the motivation for his creation of a 'mythology'. While the language developed, he needed speakers, history for the speakers and all real dynamics, like war and migration: "It was primarily linguistic in inspiration and was begun in order to provide the necessary background of 'history' for Elvish tongues".

The Elvish languages underwent countless revisions in grammar, mostly in conjugation and the pronominal system. The Elven vocabulary was not subject to sudden or extreme change; except during the first conceptual stage c. 1910–c. 1920. Tolkien sometimes changed the "meaning" of an Elvish word, but he almost never disregarded it once invented, and he kept on refining its meaning, and countlessly forged new synonyms. Moreover, Elven etymology was in a constant flux. Tolkien delighted in inventing new etymons for his Elvish vocabulary.

From the outset, Tolkien used comparative philology and the tree model as his major tools in his constructed languages. He usually started with the phonological system of the proto-language and then proceeded in inventing for each daughter language the many mechanisms of sound change needed.