What 1942 C.S. Lewis work is written as letters from a senior demon to a junior tempter?

The Screwtape Letters is C.S. Lewis’s 1942 work written as advice from a senior demon to a junior tempter.

The book consists of fictional letters from Screwtape, an experienced demon, to his nephew Wormwood, who is assigned to influence a human “patient.” Lewis reverses ordinary moral instruction by presenting temptation from the tempter’s point of view. The device lets him examine pride, distraction, social pressure, resentment, and spiritual self-deception.

The letters first appeared in the Anglican newspaper The Guardian in 1941, and the collected book was published in 1942. Lewis later found the project emotionally unpleasant because sustaining the demonic perspective affected his own mood. The work is sometimes mistaken for a conventional story with a continuous plot, but its structure is primarily epistolary: each chapter is a separate letter that develops Screwtape’s counsel.