Which C.S. Lewis work was adapted from his radio talks broadcast during World War II?

Mere Christianity was adapted from C.S. Lewis’s radio talks broadcast during World War II.

The talks were delivered for the BBC between 1941 and 1944, when Britain was at war. Lewis was invited to explain Christian belief in language accessible to a broad radio audience, and his calm, logical style made the broadcasts widely influential.

The talks were later revised and collected in book form as Mere Christianity. The title refers to the common core of Christian beliefs shared across many major Christian traditions, rather than to a particular denomination. Lewis organized the material around morality, Christian doctrine, and the practical meaning of Christian faith.

The work is not a transcript of a single wartime speech and was not originally published as one complete book. Its chapters grew from several series of broadcasts and were edited into a unified volume. That origin distinguishes it from Lewis’s other apologetic books, such as The Problem of Pain and Miracles.