Which C.S. Lewis book presents Christian ideas through conversations broadcast during World War II?

Mere Christianity presents C.S. Lewis’s Christian ideas through material first delivered in radio broadcasts during World War II. The broadcasts began in 1941 for the BBC.

Lewis was invited to speak to a British public living through wartime uncertainty. His talks explained shared Christian beliefs in accessible language and were later revised and published in book form. The title refers to basic Christianity held in common across major traditions, rather than to one denomination.

The finished book is arranged in four parts: “Right and Wrong as a Clue to the Meaning of the Universe,” “What Christians Believe,” “Christian Behaviour,” and “Beyond Personality.” It is not a transcript of a single uninterrupted broadcast series, because Lewis revised and expanded the material for publication.