This is an edition of what are arguably Leibniz's three most important presentations of his metaphysical system: the Discourse on Metaphysics, from 1686, and The Principles of Nature and of Grace and The Monadology, from 1714. Based on the Latta and Montgomery translations and revised by the editor, these texts set out the essentials of Leibniz's mature metaphysical views. The edition includes an introductory essay and a set of appendices of seventeenth- and eighteenth-century texts, which help illuminate and contextualize Leibniz's ideas. Among these are extensive passages from Leibniz's Theodicy, many of which are cited in The Monadology.