Which C.S. Lewis book is based on his radio talks about Christianity?

Mere Christianity is based on C.S. Lewis’s radio talks about Christianity.

The talks were broadcast by the BBC during the Second World War, beginning in 1941. Lewis spoke to a broad public audience about shared Christian beliefs rather than presenting the distinctive doctrines of one denomination. His broadcasts were later revised and collected in book form.

Mere Christianity was published in 1952. Its major sections discuss the moral law, Christian belief, and Christian conduct. Lewis uses examples from ordinary experience and aims to explain foundational ideas in language accessible to listeners who might not have had formal theological training.

The title does not mean that Lewis was proposing a new church or denomination. “Mere Christianity” refers to the common core of beliefs historically shared by major Christian traditions. The book is therefore different from Christian Behaviour, which formed part of the original broadcast and book structure, and from later collections of Lewis’s more specialized arguments.