What was the title of J.R.R. Tolkien’s 1939 lecture that introduced the term “eucatastrophe”?

On Fairy-Stories was the title of J.R.R. Tolkien’s 1939 lecture associated with the term “eucatastrophe.”

Tolkien delivered the lecture as the Andrew Lang lecture at the University of St Andrews in Scotland. He later revised it for publication, and it became an important statement of his views about fairy stories, imagination, recovery, escape, and consolation.

In the essay, Tolkien uses “eucatastrophe” for a sudden, joyful turn in a story’s fortunes. He regarded it as more than a convenient happy ending: it is a narrative recovery that can produce a powerful sense of hope. He connected this idea with the Christian story of the Resurrection.

The title is often confused with The Monsters and the Critics, another famous Tolkien lecture, delivered in 1936 about the study of Beowulf. On Fairy-Stories is the work most directly associated with Tolkien’s discussion of fairy-story theory and eucatastrophe.