C.S. Lewis first delivered the talks later published as Mere Christianity on BBC radio.
The broadcasts began during the Second World War, when Lewis was invited to present short talks about Christian belief to a wide public audience. The first series was broadcast in 1941, followed by additional series in 1942 and 1944. Their direct, conversational style helped make difficult theological ideas accessible to listeners.
Lewis did not originally write one continuous book called Mere Christianity. The later volume brought together revised versions of the broadcast talks, along with material from related radio scripts. The title refers to the shared core of Christianity rather than to a single denomination.
Because Lewis was an Oxford academic and also preached in churches, readers sometimes identify Oxford or a chapel as the original venue. Those places were important to his life, but the famous talks began as BBC radio broadcasts, making the series an early example of mass-media religious communication.