The 10 Most Expensive Books in the World

Traité des arbres fruitiers [Treatise on Fruit Trees] by Henri Louis Duhamel du Monceau, illustrated by Pierre Antoine Poiteau and Pierre Jean François Turpin — $4.5 million

Definitely the most expensive book ever written about fruit trees (featuring sixteen different varieties!), a copy of this lush, five volume set of illustrations and text sold for about $4.5 million in 2006.