What 1942 novel by C.S. Lewis takes the form of letters from a senior demon?

The Screwtape Letters is the 1942 C.S. Lewis novel written as advice from a senior demon. The senior tempter, Screwtape, writes letters to his inexperienced nephew Wormwood about tempting a human being.

Lewis uses the unusual viewpoint to create a satirical examination of temptation, pride, distraction, self-deception, and spiritual life. Because the advice comes from a demon, the book often presents moral insight indirectly: readers infer the author’s point by recognizing the distortions in Screwtape’s counsel.

The work first appeared in serialized form in the Anglican newspaper The Guardian in 1941, and the collected book followed in 1942. It became one of Lewis’s best-known works of Christian apologetics, although its fictional format distinguishes it from his direct nonfiction arguments.

The book is sometimes grouped with The Great Divorce because both address spiritual themes, but the two works use different narrative structures. The Screwtape Letters is specifically an epistolary satire built from correspondence between demons.