What is the title of C.S. Lewis’s Christian book adapted from his wartime radio talks?

C.S. Lewis’s Christian book adapted from his wartime radio talks is Mere Christianity.

Mere Christianity developed from radio broadcasts Lewis gave for the BBC during the Second World War. The talks were delivered between 1941 and 1944 and later revised and collected in book form. Lewis presented arguments about morality, belief, Christian doctrine, and the meaning of Christian faith for a broad public audience.

The phrase “mere Christianity” refers to the central beliefs shared by major Christian traditions. Lewis was not attempting to describe every denominational difference. Instead, he used a common foundation as the starting point for discussion, which helped make the book influential among readers from different church backgrounds.

Mere Christianity is sometimes confused with The Problem of Pain, another Lewis book about Christian belief. The Problem of Pain was published in 1940 and addresses suffering, while Mere Christianity grew from the later BBC broadcasts and has a broader introductory structure.