  There is no question that the problem of evil vexed Leibniz as much as any of the problems that he engaged in the course of his philosophical career. This is manifest in the fact that the first and the last book-length works that he authored, the Philosopher's Confession (written at age 26 in 1672) and the Theodicy (written in 1709, seven years before his death) were both devoted to this problem, as well as in the fact that in the intervening years Leibniz wrote numerous short pieces on related issues––many of which may be found in Gr and will soon be available in English translations currently being undertaken by R. C. Sleigh, Jr.–– and one full-length work, the Dissertation on Predestination and Grace (DPG), which was only published in 2011.  The fact that the Theodicy was the only book-length treatise that Leibniz published during his lifetime provides further evidence of the significance that he attributed to the topic. It is therefore appropriate that it has now become an interpretive commonplace that Leibniz's concern with the problem of evil was central to his overarching philosophical concerns throughout his philosophical career.  [See Rutherford (1995) and Antognazza (2009).]  Leibniz's approach to the problem of evil became known to many readers through Voltaire's lampoon in Candide: the link that Voltaire seems to forge between Leibniz and the extravagant optimism of Dr. Pangloss continues––for better or worse––to shape the popular understanding of Leibniz's approach to the problem of evil.  In this entry we examine the two main species of the problem of evil that Leibniz addresses. The first, “the underachiever problem,” is raised by a critic who would argue that the existence of evil in our world indicates that God cannot be as knowledgeable, powerful, or good as traditional monotheists have claimed. The second, “the holiness problem,” is raised by the critic who would argue that God's intimate causal entanglements with the world make God the cause of evil. God is thereby implicated in evil to the detriment of his holiness. 