C.S. Lewis began broadcasting the talks later collected as Mere Christianity in 1941.
The BBC invited Lewis to speak to the British public during the Second World War. His first series of radio talks was broadcast in 1941, followed by further series in 1942 and 1944. The talks addressed basic Christian beliefs in language intended for a broad audience rather than a specialist theological readership.
Dorothy L. Sayers helped with the wartime BBC religious programming context, while Lewis’s talks were later edited and published in book form. The title Mere Christianity refers to the shared core of belief found across historic Christian traditions, not to a separate denomination.
The final book was assembled from several broadcast series and appeared after the war. Because readers usually encounter the material as a single book, they sometimes assume it was originally written as a conventional volume. Its origin as radio talks explains the direct, conversational style and repeated attempts to define terms clearly.