Tam Lin, also known as Tamas-Lin, Tamlane, Tamlene, Tamlin, Tambling, Tomlin, Tam-Lien, Tam-a-Line, Tam-Lyn or Tam-Lane, is a character in the legendary ballad originating from the Scottish Borders.

The story of Tam Lin revolves around the rescue of Tam Lin by his true love from the Queen of the Fairies. The motif of winning a person (or subduing an enemy) by holding him through all forms of transformation is found throughout Europe in folktales.

The story has been adapted into numerous stories, songs, and films. It is also associated with a reel of the same name, which is also known as the Glasgow Reel.

Tam Lin is listed as the 39th Child Ballad and number 35 in the Roud Folk Song Index.

Most variants begin with the warning that Tam Lin collects either a possession or the virginity of any maiden who passes through the forest of Carterhaugh. When a young woman, usually called Janet or Margaret, goes to Carterhaugh and plucks a double rose, Tam appears and asks her why she has come without his leave and taken what is his. She states that she owns Carterhaugh because her father has given it to her.

In most variants, Janet then goes home and discovers that she is pregnant; some variants pick up the story at this point. When asked about her condition, she declares that her baby's father is an elf whom she will not forsake. In some versions, she is informed of a herb that will induce abortion; in all the variants, when she returns to Carterhaugh and picks a plant, either the same roses as on her earlier visit or the herb, Tam reappears and challenges her action.

She asks him whether he was ever human, either after that reappearance or, in some versions, immediately after their first meeting resulted in her pregnancy. Tam Lin reveals that, though he was once a mortal man, he was imprisoned in Carterhaugh by the Queen of Faeries after she kidnapped him by catching him when he fell from his horse. He goes on to tell Janet that the fairies give one of their people as a teind (tithe) to Hell at midnight on every seventh Hallowe'en. He asks Janet for her help in freeing him, and receives her agreement; he then instructs her to come to the forest at the time of the tithe, during which he'll be in the company of numerous faerie knights -- he tells her that she'll recognize him by his white horse. Janet must pull him down from his horse, thus making her the one to "catch" him this time, and hold him tightly: he warns her that the fairies will attempt to make her drop him by turning him into all manner of beasts (see Proteus), but states that none of these forms will actually cause her harm. Tam Lin will eventually take the shape of burning coal; when this occurs, Janet is to throw him into a well, whereupon he will reappear as a naked mortal man whom Janet must hide. She does as she is asked and wins her knight; though her success angers the Queen of Faeries, the latter accepts her defeat.

In different variations, Tam Lin is reportedly the grandson of the Laird of Roxburgh, the Laird of Foulis, the Earl of Forbes, or the Earl of Murray. His name also varies between versions (Tam Lin being the most common) as Tom Line, Tomlin, Young Tambling, Tam-a-line and Tamlane.