Thousands of paintings contain books, but what are they trying to say? Why is the artist sleeping off the drink while the Madame reads a book in Munch’s Christmas in the Brothel? What was Gauguin saying when he painted Paradise Lost into a portrait of a friend? And why are the Cumberland girls reading The Fashionable Lover in George Romney’s portrait of them? Camplin explains how and why books became the most ubiquitous feature of our cultural lives.