Which essay by J.R.R. Tolkien presents his theory of fantasy literature?

J.R.R. Tolkien presented his theory of fantasy literature in the essay “On Fairy-Stories.”

The essay developed from Tolkien’s 1939 Andrew Lang lecture at the University of St Andrews. He argued that fairy-stories should not be dismissed as stories only for children and examined the distinctive functions of fantasy, recovery, escape, and consolation.

Tolkien also used the term “Faërie” for the wider realm in which fairy-stories operate. His discussion of “eucatastrophe,” the sudden joyful turn at the end of a story, became one of the essay’s best-known ideas. He connected that literary effect with the Christian story of the Gospel, which he regarded as the greatest eucatastrophic narrative.

The essay was first published in 1947 and later appeared with the poem “Leaf by Niggle” in the volume Tree and Leaf. It remains one of Tolkien’s most important statements about why fantasy matters.