What title was given to the C.S. Lewis book developed from his wartime BBC radio talks?

Mere Christianity was the title given to the C.S. Lewis book developed from his wartime BBC radio talks. The talks were broadcast between 1941 and 1944 and were later revised and collected in book form.

Lewis designed the broadcasts to explain shared Christian beliefs in language accessible to a general British audience. He did not present them as a denominational work, but as an argument for what he called “mere” or common Christianity. The book is arranged in sections on morality, Christian belief, and Christian conduct.

The title can be confused with The Problem of Pain, another major Lewis apologetics book published in 1940. Mere Christianity grew directly from the radio talks, while The Problem of Pain was written independently before the broadcasts.