Which C.S. Lewis novel begins with the creation of Narnia?

The C.S. Lewis novel that begins with the creation of Narnia is The Magician's Nephew.

The Magician’s Nephew was published in 1955 and is the sixth Narnia book by original publication order. Its story follows Digory Kirke and Polly Plummer, who travel between worlds using magical rings made through the experiments of Digory’s uncle, Andrew Ketterley.

The children witness the birth of Narnia when Aslan sings the world into existence. The novel also explains the origin of the wardrobe’s magical wood and introduces Jadis, who later becomes the White Witch in The Lion, the Witch and the Wardrobe.

Because of its setting in Narnia’s earliest history, later editions often place The Magician’s Nephew first in the series. That is chronological order, not publication order. Lewis himself wrote and published The Lion, the Witch and the Wardrobe first, so readers can encounter the creation story either before or after the original entry point depending on the edition.