Which C.S. Lewis book collects material first presented in wartime radio broadcasts?

Mere Christianity collects material first presented by C.S. Lewis in wartime radio broadcasts.

Lewis gave a series of talks for the BBC during the Second World War. The broadcasts were intended for a broad audience and explained basic Christian ideas without focusing on one denomination. Lewis later revised and combined the talks into the book Mere Christianity.

The book was published in 1952, after earlier printed versions of the broadcast material had appeared. It is organized around moral law, Christian belief, and the differences and common ground among Christian traditions. The title refers to what Lewis regarded as shared, central Christianity.

Mere Christianity is sometimes treated as a conventional systematic theology textbook, but it began as spoken radio talks designed for ordinary listeners. That origin helps explain its direct style, conversational examples, and emphasis on accessible argument. The work became one of Lewis’s most influential books of Christian apologetics.