Which C.S. Lewis work is his autobiography about conversion and joy?

Surprised by Joy is C.S. Lewis's autobiography about his intellectual development and conversion.

Published in 1955, the book traces Lewis’s childhood, education, reading, military service, and changing religious outlook. Its title refers to “joy,” a term Lewis used for an intense longing or desire that he believed pointed beyond ordinary experiences.

The narrative describes Lewis’s movement from childhood belief to atheism and then back toward Christianity. He became a theist in 1930 and later embraced Christianity. Lewis’s friendships with writers including J.R.R. Tolkien influenced his thinking, although the autobiography presents his development in his own terms.

Surprised by Joy is not a complete account of every part of Lewis’s life. For example, it ends before some later events, including his marriage to Joy Davidman. A Grief Observed, published in 1961, is instead a short, emotionally direct work written after Davidman’s death.