"Leaf by Niggle" is a short story written by J. R. R. Tolkien in 1938–39 and first published in the Dublin Review in January 1945. It can be found, most notably, in Tolkien's book titled Tree and Leaf, and in other places (including the collections The Tolkien Reader, Poems & Stories, A Tolkien Miscellany, and Tales from the Perilous Realm). This is notable because the book, consisting of a seminal essay called "On Fairy-Stories" and "Leaf by Niggle", offers the underlying philosophy (Creation and Sub-Creation, see below) of much of Tolkien's fantastical writings.

"Leaf by Niggle" is often seen as an allegory of Tolkien's own creative process, and, to an extent, of his own life.