Gottfried Wilhelm Leibniz is not usually regarded as a thinker who had a substantive theory of toleration. This chapter pieces together the scattered evidence to suggest otherwise. It is argued that Leibniz did have a doctrine of toleration, which operated on philosophical, theological, and pragmatic levels as part of his project for religious unification. The structure of Leibniz's philosophical arguments reflected his dependence on an idea of natural law that acted to support conceptions of toleration, in some ways far more inclusive than those of contemporaries such as Pufendorf and Locke. By reference to the primary, inalienable moral qualities of human beings, Leibniz was able to suggest that the coercion of individuals for almost any form of sincere belief was fundamentally illegitimate. There were limits to Leibniz's toleration — doctrines against natural law were emphatically not to be tolerated — but their effect was to create an unusually wide doctrine of toleration.