Which C.S. Lewis book was adapted into the 1956 film The Screwtape Letters?

No 1956 film called The Screwtape Letters was adapted from a C.S. Lewis book.

The Screwtape Letters is a 1942 Christian apologetics work presented as fictional correspondence from Screwtape, an experienced demon, to his junior nephew Wormwood. It is a book, not the title of a 1956 feature film. This distinction matters because references to adaptations and stage versions are sometimes incorrectly presented as a mid-century movie.

Lewis’s work has inspired dramatizations, audio productions, stage adaptations, and screen projects, but a 1956 film with that title is not part of the documented filmography. The book itself has also been adapted for theater, including stage productions based on the letters.

This is a verification question rather than a conventional title-identification question: the premise is false. The exact answer is that no such 1956 film exists, so none of the listed book titles can be the source of it.