Which book by C.S. Lewis describes his conversion from atheism to Christianity?

Surprised by Joy is the C.S. Lewis book that describes his conversion from atheism to Christianity. Published in 1955, it is an autobiographical account of his intellectual and spiritual development.

Lewis traces his early religious upbringing, rejection of Christianity, growing interest in mythology and literature, and eventual return to belief. He describes conversion as a process rather than a single isolated event. His friendships with Owen Barfield and J.R.R. Tolkien helped shape the discussions that influenced this change.

The book’s title refers to Lewis’s idea of “joy,” a longing or sudden experience of desire that he associated with glimpses of transcendence. It is sometimes mistaken for a conventional memoir covering every period of his life. Instead, the book concentrates on the experiences and ideas that led toward his Christian faith.