Which C.S. Lewis work was adapted from his 1940s BBC broadcasts?

Mere Christianity was adapted from C.S. Lewis’s 1940s BBC broadcasts.

Lewis delivered a series of radio talks during World War II, beginning in 1941. The broadcasts explained basic Christian ideas in language intended for a broad public audience rather than for specialists in theology.

The talks were later revised and collected into books. The resulting work, Mere Christianity, discusses morality, belief, Christian doctrine, and the meaning of conversion. Its title refers to the shared core of Christianity rather than to one particular denomination.

The work is sometimes confused with The Problem of Pain, which began as a book about suffering, or with Miracles, a later philosophical defense of the supernatural. Mere Christianity’s defining origin is its development from Lewis’s wartime radio talks.