C.S. Lewis returned to Christianity in 1931 after a period as an atheist and then a theist.
Lewis had rejected Christianity during his adolescence, but his views changed gradually through reading, philosophical reflection, and conversations with friends. He later described himself as becoming a theist before accepting Christianity specifically.
His conversations with J.R.R. Tolkien and Hugo Dyson were especially important. On 19 September 1931, Lewis and Tolkien discussed myth, Christianity, and the possibility that Christian stories could be understood as “true myth.” Lewis later wrote that he came to believe in Christ while traveling to Whipsnade Zoo with his brother Warren.
Lewis’s conversion did not instantly produce his mature public career as an apologist. His major Christian books, including The Problem of Pain and Mere Christianity, appeared during the following decade. Accounts often simplify the process, but Lewis’s own writings present it as a gradual intellectual and spiritual change.