Which 1950 novel by C.S. Lewis introduces the wardrobe doorway to Narnia?

The Lion, the Witch and the Wardrobe is C.S. Lewis's 1950 novel that introduces the wardrobe doorway to Narnia.

The story follows four siblings—Peter, Susan, Edmund, and Lucy Pevensie—who discover a passage into the magical land of Narnia through a wardrobe. Lucy is the first of the children to enter. In Narnia, the siblings encounter the White Witch, whose rule has brought a long winter, and Aslan, the great lion.

The book was the first Narnia novel Lewis published, although many modern editions number The Magician's Nephew first because that story takes place earlier in the fictional chronology. The distinction between publication order and internal chronology explains much of the disagreement about which book is “first.”

The novel became a landmark of children's fantasy and has been adapted for radio, television, stage, and film. Its title is often shortened informally to The Lion, the Witch and the Wardrobe.