Which C.S. Lewis book presents a fictional correspondence between two demons?

The Screwtape Letters presents a fictional correspondence between two demons.

The senior demon Screwtape writes advice to his inexperienced nephew Wormwood, who is assigned to tempt a human being. Lewis uses the letters to expose habits such as vanity, resentment, distraction, and spiritual complacency by describing them from the enemy’s perspective.

The book appeared in 1942 during World War II, when Lewis was already known for his religious broadcasts. Its unusual form made abstract moral ideas vivid, but it is not a handbook of demonology or a literal account of supernatural bureaucracy.

Lewis dedicated the book to J.R.R. Tolkien, although the two men had different religious backgrounds and literary approaches. The story is also distinct from The Great Divorce, which uses a bus journey between Heaven and Hell to explore choices about belief and desire.