Which C.S. Lewis book takes the form of letters from a senior demon to a junior tempter?

The Screwtape Letters is the C.S. Lewis book written as advice from a senior demon to a junior tempter.

The book was first published in 1942. Its letters come from Screwtape, an experienced tempter, to his nephew Wormwood, who is assigned to influence a human being. Lewis uses the fictional demonic viewpoint to satirize self-deception, pride, distraction, and other moral weaknesses.

The unusual viewpoint can confuse readers who assume the book presents a demon’s theology directly. Instead, the irony comes from seeing ordinary human behavior described as a strategy in a spiritual conflict. Lewis later wrote a final piece, “Screwtape Proposes a Toast,” which was published separately before being included in later editions.