Which book by C.S. Lewis grew out of his 1940s BBC radio broadcasts?

C.S. Lewis’s book Mere Christianity grew out of his 1940s BBC radio broadcasts.

Lewis delivered a series of short talks for BBC Radio during the Second World War. The broadcasts were aimed at a general audience rather than an academic one, and they presented a case for basic Christian beliefs in accessible language. Their success led Lewis to revise and combine the material in book form.

The first printed version, Broadcast Talks, appeared in 1942. A second group of talks became Christian Behaviour in 1943, and a third became Beyond Personality in 1944. In 1952, the three sections were collected and revised as Mere Christianity, the title by which the work is now best known.

The book is not a novel and does not attempt to explain every Christian denomination. Lewis deliberately focused on what he regarded as shared Christian doctrine. Readers sometimes assume the title refers to a vague or simplified religion; Lewis used “mere” to mean the common core of beliefs held across historic Christian traditions.