The correspondence between Leibniz and Samuel Clarke was the most influential philosophical exchange of the eighteenth century, and indeed one of the most significant such exchanges in the history of philosophy. Carried out in 1715 and 1716, the debate focused on the clash between Newtonian and Leibnizian world systems, involving disputes in physics, theology, and metaphysics. The letters ranged over an extraordinary array of topics, including divine immensity and eternity, the relation of God to the world, free will, gravitation, the existence of atoms and the void, and the size of the universe. This penetrating book is the first to offer a comprehensive overview and commentary on the Leibniz-Clarke correspondence. Building his narrative around general subjects covered in the exchange--God, the soul, space and time, miracles and nature, matter and force--Ezio Vailati devotes special attention to a question crucial for Leibniz and Clarke alike. Both philosophers, worried by the advance of naturalism and its consequences for morality, devised complex systems to counter naturalism and reinforce natural religion. However, they not only deeply disagreed on how to answer the naturalist threat, but they ended up seeing in each other's views the germs of naturalism itself. Vailati rigorously tracks the twists and turns of this argument, shedding important new light on a critical moment in modern philosophy. Lucid, taut, and energetically written, this book not only examines the Leibniz-Clarke debate in unprecedented depth but also situates the views advanced by the two men in the context of their principal writings. An invaluable reference to a fascinating exchange of ideas, Leibniz and Clarke makes vital reading for philosophers and historians of science and theology.