C.S. Lewis first presented the talks later collected as Mere Christianity on BBC radio.
Lewis delivered a series of wartime radio broadcasts for the BBC between 1941 and 1944. The talks addressed basic Christian beliefs in language intended for a broad public audience, including listeners who might not regularly attend church. They were later revised and collected in book form as Mere Christianity.
The work is not a complete systematic theology. Instead, Lewis uses the idea of a shared Christian moral and doctrinal core as a starting point for discussing belief, repentance, and Christian conduct. The title refers to what he presents as common ground among major Christian traditions.
The broadcasts made Lewis widely known beyond academic and literary circles. His clear speaking style and use of everyday examples helped the programs reach wartime listeners. Because the book is now more familiar than the original broadcasts, people sometimes assume it began as a conventional printed volume rather than as a radio series.