Which C.S. Lewis book is written as letters from the demon Screwtape?

The C.S. Lewis book written as letters from the demon Screwtape is The Screwtape Letters.

Published in book form in 1942, The Screwtape Letters presents a series of fictional letters from Screwtape, a senior demon, to his inexperienced nephew Wormwood. The correspondence offers advice on tempting a human known only as “the Patient.”

Lewis uses the demons’ perspective to satirize self-deception, vanity, distraction, resentment, and other habits that can damage moral and spiritual life. The device lets him discuss Christian ethics indirectly, often by having the demons misunderstand or distort goodness.

The book is sometimes confused with Lewis’s direct apologetic works, especially Mere Christianity. Unlike that book, The Screwtape Letters is an imaginative literary work presented through an invented demonic correspondence. It was adapted from letters first published in the Anglican newspaper The Guardian.