What is the name of the essay in which J.R.R. Tolkien explained the idea of “eucatastrophe”?

J.R.R. Tolkien explained the idea of “eucatastrophe” in his essay On Fairy-Stories. He delivered the essay as the Andrew Lang lecture at the University of St Andrews in 1938, and it was later published in revised form.

Tolkien used “eucatastrophe” for the sudden turn from impending disaster to joy or deliverance. He described it as the true form of the fairy-story’s ending, while emphasizing that it is not a denial of sorrow or suffering. The term combines the Greek prefix eu-, meaning good, with catastrophe.

The concept is often reduced to “a happy ending,” but Tolkien’s meaning is more specific. He connected eucatastrophe with a glimpse of joy beyond the ordinary course of events. He also discussed the “mythical” and “consolatory” functions of fairy-stories, subjects that made the essay important to later fantasy criticism.