Which book by C.S. Lewis is a fictional exchange of letters between demons?

The Screwtape Letters is a fictional exchange of letters between demons created by C.S. Lewis.

The book consists of advice from Screwtape, a senior demon, to his inexperienced nephew Wormwood. Their correspondence discusses temptation, pride, distraction, relationships, and the habits that can shape a person’s moral life.

Lewis wrote the letters during the early years of World War II. The work first appeared in serial form in the Anglican newspaper The Guardian in 1941, and it was published as a book later that year. Its satirical form lets Lewis examine human behavior from the viewpoint of Hell.

The book is sometimes mistaken for a conventional theological treatise, but it is fiction and satire. Lewis later found the sustained demonic viewpoint uncomfortable to maintain and did not write a sequel. The Screwtape Letters became one of his most widely read Christian works.