Which C.S. Lewis book presents fictional letters from a senior demon to a junior tempter?

The Screwtape Letters is the C.S. Lewis book presented as letters from a senior demon to a junior tempter.

The senior demon, Screwtape, writes advice to his inexperienced nephew Wormwood about tempting a human being. The fictional correspondence uses reverse perspective: readers see ordinary human weaknesses and spiritual choices described from the viewpoint of Hell’s bureaucracy.

Lewis first published the work in book form in 1942. The letters had previously appeared in the Anglican newspaper The Guardian, which printed them in 1941. The book is an imaginative work of Christian apologetics and satire, not a conventional narrative told by a human protagonist.

A common mix-up is The Great Divorce, another Lewis work with an afterlife setting. That book uses a bus journey and conversations between the inhabitants of Heaven and Hell. The Screwtape Letters is distinguished by its epistolary form and its two demon characters.