Lewis said that his publisher chose the order in which his Narnia books were published, and when asked in what order they should be read, if possible, he provided this sequence: The Magician's Nephew
The Lion, the Witch and the Wardrobe
The Horse and His Boy
The Silver Chair
Prince Caspian
The Voyage of the "Dawn Treader"
The Silver Chair
The Last Battle

Each novel can stand on its own, without being read in any particular order, but the sequence Lewis preferred is chronological, from the beginning of Narnia's world to its ending.

The Magician's Nephew was written after The Lion, the Witch and the Wardrobe, so Lewis had the task of making his account of the beginning of Narnia's world match the events that would later occur in The Lion, the Witch and the Wardrobe. The Magician's Nephew provides explanations for the origins of the...