Which C.S. Lewis book explains Christianity through a series of BBC radio talks?

Mere Christianity explains Christianity through C.S. Lewis’s series of BBC radio talks.

Lewis delivered the talks during the Second World War, beginning in 1941, when the BBC sought accessible religious broadcasts for the public. He spoke about morality, belief, and the central ideas shared by historic Christian traditions. The broadcasts were later revised and collected into book form, first as separate volumes and then as Mere Christianity.

The title refers to what Lewis regarded as common or “mere” Christianity rather than a single denomination. The book is therefore not a denominational manual, and it does not present every Christian doctrine in equal detail. Its structure moves from moral experience toward Christian belief and then discusses virtues and Christian conduct.