Surprised by Joy: The Shape of My Early Life is a partial autobiography by C.S. Lewis that describes his conversion to Christianity. Unlike typical autobiographies, this book contains less detail about specific events because Lewis's primary aim was not historical documentation. Instead, he sought to identify and describe the events surrounding his accidental discovery of, and consequent search for, the phenomenon he labeled "Joy." This word was the best translation he could make of the German idea of Sehnsucht, or longing.

Although the book is not devoid of information about Lewis's life, the principal theme is Joy as he defined it. This Joy was a longing so intense for something so good and so high up that it couldn't be explained with words. Throughout his life, he was struck with "stabs of joy" and finally finds what it's for at the end.

Lewis recounts his early years with a mix of amusement and pain, including his experiences at Malvern College in 1913, aged 15. He described the school as "a very furnace of impure loves" but defended the practice as "the only chink left through which something spontaneous and uncalculating could creep in."

The book's last two chapters cover the end of his search as he moves from atheism to theism and then from theism to Christianity, ultimately discovering the true nature and purpose of Joy and its place in his life.

It is important to note that the book is not connected with his unexpected marriage later in life to Joy Gresham. The marriage occurred long after the period described, though not long after the book was published. His friends were quick to notice the coincidence, remarking that he'd really been "Surprised by Joy."

The title also alludes to Wordsworth's poem, "Surprised by Joy - Impatient As The Wind," which relates an incident when Wordsworth forgot the death of his beloved daughter.