Leibniz’s “Experiments in Theodicy,” otherwise experiments in justification of God, is the most important study of the question of how evil is possible in a world that God does not intend to leave. Leibniz examines the concepts of omnipotence, justice and mercy of God and shows the existential meaning of evil and death as the possibility of personal choice. Evil is irrevocable, but victory over it is the only guarantee of personality development. The problems posed by Leibniz are important for the debates of modern philosophy about religion and atheism, about freedom and necessity, about inevitably evil choices (“the trolley problem”) and moral testing and the study of other tantalizing questions.