"Mere Christianity" is a theological book by C.S. Lewis, first published in 1952. It originated from a series of radio talks given during World War II, aiming to explain the core beliefs of Christianity to a general audience. Lewis emphasizes the common ground among different Christian denominations and presents a rational case for faith. The book is divided into four sections, covering topics such as morality, Christian behavior, and the nature of God. Lewis argues that Christianity offers a unique solution to human problems and invites readers to explore the implications of faith in their lives.