A “universal genius”—mathematician, scientist, diplomat, historian, ecumenist, and philosopher—Leibniz was “the pathfinder of the German Enlightenment.” For the last forty years of his life, he worked for the House of Hanover, principally as the royal librarian. A devout Lutheran, Leibniz, in an age of increasing determinism and materialism, strove to envision a worldview that was rational, hopeful, and spiritual. Reality for Leibniz was composed of an infinite number of individual spiritual substances (“monads,” from the Greek word meaning “one”), arranged in an ascending order of consciousness from nearly nothing to God (“the Supreme Monad”). Created by God, this is “the best of all possible worlds,” since in it an infinite being chose to honor the limitations of finitude. So-called evils (material, mental, or moral) contribute to the ultimate good of the universe. This intelligent and benevolent world is rational, and all things in it exhibit a pre-established harmony, or “unity.” Such a universe invites ethical action that is both personal and social, both thoughtful and charitable.