Which C.S. Lewis work was adapted from his BBC radio broadcasts about Christianity?

Mere Christianity was adapted from C.S. Lewis’s BBC radio broadcasts about Christianity. The talks were delivered during the Second World War, beginning in 1941, and were later revised and collected into book form.

Lewis first published the material in three parts: Broadcast Talks in 1942, Christian Behaviour in 1943, and Beyond Personality in 1944. The unified book Mere Christianity appeared in 1952. It presents a general case for shared Christian beliefs rather than defending one denomination’s distinctive doctrines.

The title refers to what Lewis regarded as the common or central ground of Christianity. The work is often confused with The Problem of Pain because both discuss religious belief, but Mere Christianity grew directly from radio talks intended for a broad public audience.