In Monads, Composition and Force, Richard T. W. Arthur goes against a long trend of idealistic interpretations of Leibniz’s thought by taking seriously his claim of introducing monads to solve the problem of the composition of matter and motion. Offering a fresh interpretation of Leibniz’s theory of substance, Arthur argues that although monads are presupposed as the principles making actual each of the infinite parts of matter, bodies are not composed of them. Leibniz conceives the monads as enduring primitive forces, whose modifications are the derivative forces of physics, from which bodies and their motions result as real phenomena. Arthur also analyses Leibniz’s engagement with seventeenth century atomism, examines the scholastic metaphysics of the plurality of forms, and connects Leibniz’s contributions to biological science with the dynamical foundations he provides for modern physics.