What was the original medium of the talks that became C.S. Lewis’s Mere Christianity?

The talks that became C.S. Lewis’s Mere Christianity were originally BBC radio broadcasts.

Lewis delivered a series of radio talks for the BBC during the Second World War. The first series was broadcast in 1941, followed by additional series in 1942 and 1944. The talks addressed basic Christian beliefs in language intended for a broad British audience rather than for specialists.

After revision and publication in book form, the material became Mere Christianity. The title refers to the shared core of belief held across the major Christian traditions, rather than to a separate denomination. The book is organized around morality, Christian belief, and practical implications of faith.

Some readers assume the work began as a conventional book or a sequence of university lectures. Its broadcast origin explains its direct, conversational style and its effort to communicate through radio to listeners living through wartime uncertainty.