Which C.S. Lewis book presents his BBC radio talks later collected as Mere Christianity?

Mere Christianity presents C.S. Lewis’s BBC radio talks on Christian belief.

The talks were broadcast during the Second World War, beginning in 1941, when Lewis was already known for his clear public speaking and apologetic writing. He addressed subjects such as morality, Christian doctrine, and the meaning of faith for a general audience rather than an academic one.

The material was revised and published in book form in stages. The first collection, Broadcast Talks, appeared in 1942; it was followed by Christian Behaviour in 1943 and Beyond Personality in 1944. The three parts were later combined under the title Mere Christianity in 1952.

The title refers to the shared core of beliefs held by major Christian traditions, not to a separate denomination. Readers sometimes assume the book was originally written as one continuous volume, but it grew from a sequence of wartime broadcasts and later editorial revisions.