Which C.S. Lewis book is a memoir of his conversion to Christianity?

Surprised by Joy is C.S. Lewis’s memoir of his conversion to Christianity.

Published in 1955, Surprised by Joy recounts Lewis’s intellectual and spiritual development from childhood through his return to Christianity. The book describes his changing responses to literature, mythology, philosophy, and religious belief. Its title uses Lewis’s term “Joy” for an intense, often fleeting longing that he associated with experiences of beauty and transcendence.

Lewis had become an atheist in his adolescence, later moving toward theism and then Christianity. He described his conversion to theism in 1929 and his conversion to Christianity in 1931. The memoir is not a conventional day-by-day autobiography, and it does not cover his whole life. Readers sometimes confuse it with Mere Christianity, which developed from wartime radio talks and presents a systematic case for Christian belief.