Melian is a fictional character in J.R.R. Tolkien's Middle-earth legendarium. She appears in The Silmarillion, The Children of Húrin, Beren and Lúthien, and in several stories within The History of Middle-earth series. An early version of Melian is found in The Book of Lost Tales II, part of The History of Middle-earth, where her characterization differs significantly. The final version of the character is presented as a Maia, a lesser class of powerful divine beings in Tolkien's legendarium known as the Ainur, who takes the form of an Elf and becomes the loyal queen consort of Elu Thingol.

Melian is an important character in the First Age of Middle-earth, and an essential part of the ancestral backgrounding of the interracial romances between her daughter Lúthien and the mortal Man Beren, as well as that of her descendants Aragorn and Arwen. Commentators have analysed the character's mystical nature, as well as her role as a forerunner of the Elf-queen Galadriel in The Lord of the Rings.

Now Melian had much foresight, after the manner of the Maiar; and when the second age of the captivity of Melkor had passed, she counselled Thingol that the Peace of Arda would not last for ever. He took thought therefore how he should make for himself a kingly dwelling, and a place that should be strong, if evil were to awake again in Middle-earth; and he sought aid and counsel of the Dwarves of Belegost. They gave it willingly, for they were unwearied in those days and eager for new works; and though the Dwarves ever demanded a price for all that they did, whether with delight or with toil, at this time they held themselves paid.

Melian is an angelic being, a Maia close to the godlike Valië, the Queen of the Earth, Yavanna. She originally tended fruit trees in the gardens of Lórien and served the Valier Este and Vana prior to her departure for Middle-earth. She is defined by her beauty, her connection to the natural world, her gifts of foresight and wisdom, and especially her "angelic and haunting singing". It is said that she arrives in Middle-earth to teach its birds to sing, and dwells in the forest of Nan Elmoth, to the east of Doriath in Beleriand. Because she is from Valinor, her face carries the strength and splendour of the light of Valinor when she arrives in Middle-earth, much like the Noldor who had seen the light of the Two Trees. In Nan Elmoth, she meets her future husband, the Elf Prince Elwë, while she is singing with the nightingales one day. It was then that Elwë, being "filled with love" for Melian, falls under an enchantment and utterly forgets his people the Sindar, wishing instead to spend the rest of his years with her. Taking the form of an elf and thus subjecting herself to the limits of physical embodiment, Melian spends many years in solitude with Elwe, who is thought lost to his people in Nan Elmoth until the couple re-emerge into Middle-earth society.

Melian and her husband, now known as Elu Thingol, settle in Beleriand, and establish a realm called Doriath, which they rule over as its monarchs. Their only daughter, Lúthien, is the most beautiful person who ever lived in Middle-earth. Weaving "much magic and mystery" around Thingol's halls, Melian uses her vast powers to shroud Doriath in an impenetrable, invisible barrier known as the Girdle of Melian to protect them from Morgoth's forces. It prevents anyone from entering without her or Thingol's permission, bewildering and confusing travellers and wanderers, or driving them mad. The Girdle of Melian proves to be stronger than any power except unselfish love as the mortal Man Beren, who falls in love with her daughter, manages to overcome it. As a divine being in Tolkien's legendarium, Melian's bloodline which is carried on from the marriage between Beren and Lúthien represents "a strain of the Ainur who were with Ilúvatar before Eä": her descendants include Elwing, Elrond, Arwen, Elendil, and Aragorn.

Said to be wiser than "any child of Middle-Earth", Melian is known for her insights into the future, though her counsel is repeatedly left unheeded. In The Children of Húrin, Melian is depicted as trying in vain to "avert the evil that was prepared in the thought of Morgoth": she attempts to convince Morwen against leaving the safety of Doriath, advises Túrin on the best course of action, and warns Beleg not to take up Anglachel, a cursed blade forged by the Dark Elf Eöl. She does convince Húrin to come to terms with his grief over the tragic fate of his family, after he goes on a violent rampage fuelled by rage and bitterness. Thingol himself seldom heeds her advice or warnings; this leads to disaster when his greed for the Silmaril retrieved from Morgoth's crown triggers a series of events which culminates in his own death and the fall of Doriath. Following Thingol's passing, she confers with Lúthien and Beren one final time, before returning to Valinor on her own.

The name "Melian" means Beloved in Tolkien's constructed language of Sindarin. In Quenya, another of Tolkien's languages, her name is "Melyanna", signifying "Dear Gift" or "Gift of Love" (Q. melya, "dear, lovely" < Q. mel-, "love"; Q. anna, "gift").

Tolkien had given Melian other names throughout the development process of his legendarium. She appears in The Book of Lost Tales Part One as Tindriel or Wendelin in Quenya, and in a Gnomish dictionary as Gwendeling or Gwendhiling. Within the story of The Book of Lost Tales, Vëannë and Ausir argued whether she should be called Wendelin or Gwendeling. These names were reintroduced into the 2017 book Beren and Lúthien, an extended story about the tale of Lúthien and Beren.