C.S. Lewis gave the BBC broadcasts later adapted into Mere Christianity between 1941 and 1944.
The broadcasts were delivered during the Second World War, when Lewis was already known in Britain for Christian talks and essays. He spoke to a broad radio audience rather than addressing only specialists, explaining shared Christian beliefs in accessible language.
The material appeared in stages and was later revised and collected as a book. Mere Christianity is not a transcript of one uninterrupted lecture series; it brings together material from Broadcast Talks, Christian Behaviour, and Beyond Personality. Lewis used the phrase “mere Christianity” for the common core of beliefs historically shared by major Christian traditions.
The work is therefore both a wartime broadcasting project and a later book. Readers sometimes date the book itself to the first broadcast year, but the broadcasts continued through 1944 and the collected structure developed afterward.