Which C.S. Lewis book was written as fictional letters from a demon?

The Screwtape Letters was written as fictional letters from a demon.

Published in book form in 1942, The Screwtape Letters consists of correspondence from Screwtape, a senior demon, to his inexperienced nephew Wormwood. The letters discuss methods of temptation and human weakness from the demons’ deliberately distorted perspective.

C.S. Lewis used the unusual viewpoint to create irony: readers are expected to recognize the moral errors that the demons treat as useful strategies. The book is therefore not a practical guide to wrongdoing, but a Christian satire about pride, distraction, resentment, and self-deception.

The work began as a series of letters published in the Anglican newspaper The Guardian. Lewis later collected them into a book and added a concluding piece, “Screwtape Proposes a Toast,” in later editions. The title is sometimes confused with The Great Divorce, another Lewis book involving a supernatural setting, but The Screwtape Letters is specifically an epistolary work.