Which C.S. Lewis book was published in 1942 as a demonic correspondence?

The Screwtape Letters was the C.S. Lewis book published in 1942 as a demonic correspondence.

The book consists of letters from Screwtape, a senior demon, to his inexperienced nephew Wormwood. Screwtape offers advice about tempting a human patient, allowing Lewis to present moral and spiritual observations from an intentionally inverted perspective.

Lewis originally published the letters as a series in the Anglican newspaper The Guardian in 1941. The collected book followed in 1942. Its unusual form made abstract questions about temptation, pride, distraction, and repentance vivid and accessible.

A common mix-up is to call it a novel in the ordinary sense. It has a sustained fictional situation, but its structure is epistolary: the story is delivered through correspondence. The imagined demons are not presented as reliable authorities; their advice exposes the weaknesses Lewis wanted readers to recognize.