Which C.S. Lewis book was adapted from his BBC wartime radio talks?

Mere Christianity was adapted from C.S. Lewis’s BBC wartime radio talks.

Lewis delivered a series of talks on Christian belief for BBC Radio during the Second World War. The broadcasts began with “Right and Wrong: A Clue to the Meaning of the Universe” in 1941, and later talks were revised and collected in book form. The resulting work, Mere Christianity, became one of Lewis’s best-known religious books.

The title refers to the shared core of Christian belief rather than to one denomination. Lewis organized the material around moral law, Christian doctrine, and practical Christian conduct, presenting an argument intended for a broad audience.

Mere Christianity is not a transcript published unchanged from a single broadcast series. Lewis revised and expanded the talks, and the book’s sections reflect the development of material delivered across several broadcast periods. That history distinguishes it from books Lewis wrote originally as continuous essays.