Which C.S. Lewis book was published in 1945 as a satirical correspondence between demons?

The Screwtape Letters was published by C.S. Lewis in 1945 as a satirical correspondence between demons. The book consists of letters from the senior demon Screwtape to his inexperienced nephew Wormwood.

Screwtape advises Wormwood about tempting a human being, whom the letters call “the Patient.” Lewis presents the advice from a demonic perspective, allowing ordinary moral failures and spiritual distractions to appear in an ironic, reversed light.

The work began as a series published in the Anglican newspaper The Guardian during the Second World War. It became one of Lewis’s most popular religious books and is often read as a study of temptation, pride, distraction, and self-deception.

The book is sometimes mistaken for a conventional fantasy novel because it uses invented demons and a fictional correspondence format. Its main mode is satire, and its setting is a symbolic spiritual conflict rather than the fictional world of Narnia.