C.S. Lewis titled his 1952 book of Christian apologetics Mere Christianity.
The book developed material from radio talks Lewis gave for the BBC during World War II. The broadcasts were delivered in several series between 1941 and 1944 and aimed to explain core Christian ideas in language accessible to a broad audience rather than to one denomination.
Lewis later revised and combined the talks into book form. Mere Christianity is organized around arguments about morality, Christian belief, and the nature of Christian practice. Its title refers to what Lewis regarded as shared or common Christianity, not to a separate denomination.
Readers sometimes confuse the book with The Problem of Pain, another major apologetic work by Lewis. The Problem of Pain was published in 1940 and addresses suffering, while Mere Christianity grew principally from the wartime broadcasts.