Mithril is a fictional metal from J. R. R. Tolkien's Middle-earth fantasy writings. It is silvery and stronger than steel but much lighter in weight. The author first wrote of it in The Lord of the Rings, and it was retrospectively mentioned in the second, revised edition of The Hobbit in 1966. In the first 1937 edition, the mail shirt given to Bilbo was described as being made of "silvered steel".

In The Lord of the Rings, Tolkien writes that mithril was found only in Khazad-dûm (Moria) in Middle-earth, where it was mined by the Dwarves. However, in Unfinished Tales he writes that it was also found in Númenor.

The name mithril comes from two words in Sindarin — mith, meaning "grey", and ril meaning "glitter". The metal's Quenya name is mistarille. Mithril was also called "true-silver" or "Moria-silver"; the Dwarves had their own secret name for it.