Which C.S. Lewis book is made up of letters from a senior demon to a junior tempter?

The Screwtape Letters is made up of letters from a senior demon to a junior tempter.

Published in book form in 1942, The Screwtape Letters presents a fictional correspondence from Screwtape, an experienced demon, to his nephew Wormwood. The letters offer advice on tempting a human being and are written as a satirical inversion of Christian spiritual guidance.

Lewis uses the demonic viewpoint to examine distraction, vanity, resentment, social pressure, and self-deception. Because the advice is deliberately misleading, readers are expected to infer the moral lessons by reversing Screwtape’s recommendations.

The work is an epistolary novel, meaning that it is told through letters. It is not a collection of letters written by Lewis to a real person. The imaginative form helped make serious religious and psychological themes accessible to a wide readership.