Which C.S. Lewis book takes the form of letters from a demon advising his nephew?

The C.S. Lewis book written as letters from a demon advising his nephew is The Screwtape Letters. Lewis published the work in 1942, presenting a series of fictional letters from the senior demon Screwtape to the younger demon Wormwood.

The book uses satire to examine temptation, distraction, pride, resentment, and self-deception. Because the advice is presented from the viewpoint of demons, the reader must infer the moral and spiritual lessons from their distorted perspective.

Lewis originally published the letters in a periodical before they appeared as a book. The unusual format helped make complex theological and ethical ideas accessible to general readers. It also made the work one of Lewis’s most widely recognized Christian writings.

The book is sometimes confused with The Great Divorce, another Lewis work about the afterlife and spiritual choices. The Screwtape Letters is distinctive because its entire central structure consists of correspondence between demons.