C.S. Lewis converted to Christianity in 1931 after a long period in which he described himself as an atheist. His return to belief developed through conversations and friendships, especially with J.R.R. Tolkien and Hugo Dyson.
Lewis had already moved from atheism toward theism before becoming a Christian. He later recalled that his conversion to theism occurred in 1929, while his conversion to Christianity took place in 1931. These two dates are often confused because they describe different stages of his intellectual and religious development.
Lewis described his conversion in autobiographical works including Surprised by Joy. His renewed Christian faith became central to his later writing, including The Problem of Pain, Mere Christianity, and the Narnia books.
The change did not immediately make Lewis a public apologist. His reputation as a Christian broadcaster and writer grew during the Second World War, particularly through his BBC talks. The year 1931 therefore marks a personal turning point that preceded his public fame.