Which C.S. Lewis book adapts his wartime radio talks about Christianity?

Mere Christianity adapts C.S. Lewis’s wartime radio talks about Christianity. The broadcasts were delivered for the BBC during the Second World War and were later revised and collected in book form.

Lewis aimed to explain beliefs shared by many Christian traditions rather than defend one denomination. The book discusses morality, belief, Christian doctrine, and the meaning of conversion. Its title refers to what Lewis regarded as the common core of historic Christianity.

The book is sometimes described as a direct transcript, but the published text was edited and reorganized from the broadcasts. The work became one of Lewis’s most influential apologetic books, alongside The Problem of Pain and Miracles. It also helped establish him as a prominent public religious speaker in Britain.