What is the name of C.S. Lewis's Christian apologetics book adapted from BBC radio talks?

C.S. Lewis’s Christian apologetics book adapted from BBC radio talks is Mere Christianity. The book grew out of a series of wartime broadcasts Lewis delivered for the BBC between 1941 and 1944.

The talks were designed for a broad audience during World War II and explained basic Christian beliefs without focusing on one denomination. Lewis discussed morality, human nature, repentance, and the central doctrines shared by many Christian traditions. The broadcast material was later revised and collected into book form, with Mere Christianity appearing in 1952.

The title is often confused with The Problem of Pain, another Lewis apologetics work published in 1940, or with Miracles, published in 1947. Mere Christianity is distinctive because its origin lies in radio talks intended for ordinary listeners rather than in a book written first for an academic audience.