ABSTRACTThis paper expounds and critically assesses G. W. Leibniz’s mature theory of the cohesion of material bodies. Leibniz’s later view of cohesion was forged in polemical engagement with the views of John Locke and the Dutch natural philosopher Nicolaas Hartsoeker and it is in Leibniz’s response to Locke in his New Essays on Human Understanding, and especially his correspondence with Hartsoeker, that the theory is revealed. After setting out Locke’s theory of solidity and cohesion, the paper examines Leibniz’s response to (...) Locke in the New Essays. It then proceeds to the mechanical theory of conspiring motions developed in the Hartsoeker correspondence. The final section of the paper poses three problems for Leibniz’s theory – explanatory, empirical, and conceptual. (shrink)