Which C.S. Lewis book features the character Screwtape giving advice to a junior demon?

The C.S. Lewis book featuring Screwtape is The Screwtape Letters. It is a satirical work presented as a series of letters from an experienced demon to a younger demon named Wormwood.

Screwtape advises Wormwood on how to tempt and mislead a human being. Lewis reverses the expected viewpoint: readers see human weaknesses, distractions, and moral choices described from the perspective of Hell’s bureaucracy. The result is a work of Christian apologetics that uses irony rather than a conventional narrative.

The letters first appeared in the Anglican newspaper The Guardian in 1941. They were later published as a book, with a preface by Lewis explaining some of the difficulties of writing from a demonic viewpoint. The work quickly became one of his most popular religious books.

Readers sometimes confuse it with The Great Divorce, another Lewis book about spiritual realities. The two works differ in form: The Screwtape Letters consists of correspondence, while The Great Divorce is a fictional journey and theological thought experiment.