Which C.S. Lewis book is based on his 1940s BBC radio broadcasts?

Mere Christianity is the C.S. Lewis book based on his 1940s BBC radio broadcasts.

Lewis delivered a series of wartime radio talks for the BBC between 1941 and 1944. The talks were intended for a broad audience and presented basic Christian ideas in accessible language. Lewis did not initially use the later book title for the broadcasts; the material was revised and published in separate volumes before being collected as Mere Christianity in 1952.

The book is organized around common moral awareness, Christian belief, and practical consequences of faith. Lewis’s aim was not to argue for one denomination but to explain what he saw as central beliefs shared by historic Christianity. The phrase “mere Christianity” refers to that shared core.

The work became one of Lewis’s most influential apologetic books. Its conversational style reflects its origin in radio, although the printed text is edited and arranged rather than being a simple transcript. The broadcasts were made during World War II, when radio allowed Lewis’s arguments to reach listeners across Britain.