The Book of Dust is a trilogy of fantasy novels by Philip Pullman, which expands his trilogy His Dark Materials. The books further chronicle the adventures of Lyra Belacqua and her battle against the theocratic organisation known as the Magisterium, and shed more light on the mysterious substance called Dust.

The first book, La Belle Sauvage, was published in October 2017, and is set 12 years before Northern Lights. It describes how the 11-year-old Malcolm Polstead and the 15-year-old Alice protect the infant Lyra; leading to her being in the care of Jordan College. It introduces the research by academics and other free-thinkers into Dust, a mysterious subatomic particle related to consciousness, and the origins of Lyra's alethiometer.

The second book, The Secret Commonwealth, was published on 3 October 2019 and is set after the events in the original trilogy with Lyra as a twenty-year-old undergraduate. Work on the third book in the series had not commenced at that time.

Pullman has said that the trilogy addresses consciousness: "Perhaps the oldest philosophical question of all: are we matter? Or are we spirit and matter? What is consciousness if there is no spirit? Questions like that are of perennial fascination and they haven’t been solved yet, thank goodness." He added that the series might be slightly darker than the original, and quipped that it could alternatively be titled "His Darker Materials".