What was the title of C.S. Lewis’s 1940 book about Christian belief and demonic correspondence?

The Screwtape Letters is C.S. Lewis’s 1940 book presented as correspondence about Christian belief and temptation.

The book consists of letters from Screwtape, an experienced demon, to his inexperienced nephew Wormwood. Screwtape offers advice on how to influence a human being, whom he calls “the Patient,” away from faith and moral attention.

Lewis reverses the usual viewpoint: readers hear demonic strategy while being expected to recognize its errors. This allows the book to examine pride, distraction, resentment, self-deception, and ordinary habits without presenting a conventional theological treatise.

The work first appeared in serialized form in the Anglican newspaper The Guardian before being collected as a book in 1942. Lewis later said he found the tone exhausting to sustain. The title is sometimes confused with Mere Christianity, another work based partly on Lewis’s wartime religious broadcasts, but the two books use entirely different forms.