Which BBC radio broadcast series formed the basis of C.S. Lewis's Mere Christianity?

C.S. Lewis's Mere Christianity was based on a series of BBC radio broadcast talks.

Lewis delivered the talks during the Second World War, beginning in 1941. The BBC invited him to explain Christian belief to a broad public audience, and his broadcasts were heard in Britain during a period of wartime uncertainty. He later revised the talks for print.

The published book was assembled from several broadcast series. The first section developed from talks originally issued as The Case for Christianity. These were followed by Christian Behaviour and Beyond Personality. The combined work appeared as Mere Christianity in 1952.

The title refers to the shared core of belief found across historic Christian traditions, rather than to one denomination. Lewis was an Anglican layman and did not present the book as a complete account of every Christian doctrine. A frequent misunderstanding is that the book is a transcript of one continuous program; it is instead a revised collection of talks delivered in separate wartime series. Its conversational style reflects its radio origin.