Which C.S. Lewis book originated from his 1940s BBC radio talks?

Mere Christianity originated from C.S. Lewis’s BBC radio talks and was later published as a book.

Lewis delivered the first series of talks in 1941, followed by further broadcasts in 1942 and 1944. The talks were intended for a broad wartime audience and presented basic Christian beliefs in language designed to be accessible across denominational divisions.

The material was revised and collected in book form in 1952. Mere Christianity is organized around themes including morality, Christian belief, and the idea of transformation through faith. It is an apologetic work rather than a narrative or a formal denominational catechism.

The book is sometimes mistakenly treated as a direct transcript of a single broadcast series. In fact, Lewis revised the radio material for print, and the final volume combines material from multiple sets of talks. Its title refers to the shared core of Christianity rather than to a separate church denomination.