Which C.S. Lewis work was originally delivered as radio broadcasts during World War II?

Mere Christianity was originally delivered as radio broadcasts during World War II.

Lewis gave a series of BBC radio talks between 1941 and 1944 at the invitation of broadcaster James Welch. The talks were designed for a broad audience during wartime and presented shared Christian ideas rather than the distinctive doctrines of one denomination. Lewis later revised and expanded the broadcasts into books.

The material was eventually published in three parts: Broadcast Talks in 1942, Christian Behaviour in 1943, and Beyond Personality in 1944. These sections were combined as Mere Christianity in 1952. The book discusses moral law, Christian belief, and the virtues and claims of Christianity.

The work is not a transcript of a single broadcast and was not first published as one complete volume. Lewis’s clear, conversational radio style helped make the later book one of his most widely read apologetic works.