C.S. Lewis identified his conversion to Christianity as having been completed in 1931.
Lewis had moved through several stages of belief. As a young man he rejected Christianity and described himself as an atheist, but conversations with friends and colleagues—including J.R.R. Tolkien and Hugo Dyson—helped him reconsider Christian ideas. He became a theist in 1930 and later embraced Christianity.
In a letter, Lewis described the decisive change as taking place during a nighttime journey to Whipsnade Zoo in September 1931. He wrote that he went to the zoo not believing in God and returned believing in Christianity. He later explained these events in autobiographical works such as Surprised by Joy.
The year can be confused with 1929, when Lewis said he surrendered and acknowledged God’s existence. His Christian conversion is generally dated to 1931, while his earlier move from atheism to theism belongs to 1930.