On Fairy-Stories is an essay written by J. R. R. Tolkien, first published in Essays Presented to Charles Williams, Oxford University Press, 1947. It was subsequently published with Leaf by Niggle in Tree and Leaf.

The essay is significant because it contains Tolkien's explanation of his philosophy on fantasy and thoughts on the crafting of mythologies.

The key points of this philosophy are:

• Fairy-Stories are not the same thing as fairy tales (e.g., Grimm's Fairy Tales).
• Fairy-Stories are not stories about fairies, etc.; they are stories about people and the effects on their lives of interactions with such things.