What title did C.S. Lewis give the book developed from his BBC religious broadcasts of 1941–1944?

C.S. Lewis titled the book developed from his BBC religious broadcasts Mere Christianity.

Lewis delivered a series of radio talks during the Second World War, beginning with The Case for Christianity in 1941. Further broadcasts followed in 1942 and 1944. The talks were intended to explain and defend basic Christian beliefs to a broad audience rather than promote one particular denomination.

After the broadcasts, Lewis revised and combined the material into a book. Mere Christianity was published in 1952, with the title referring to the common beliefs shared by historic Christian traditions. Its sections discuss morality, Christian theology, and the doctrine of the Trinity.

The book is not a transcript of every broadcast in its original form. Lewis edited the material for print and shaped it into a connected argument. The work became one of his most widely read Christian apologetics books, alongside The Problem of Pain and Miracles.