 Perhaps no other medieval Jewish philosopher has been so maligned over the centuries as Gersonides (Levi ben Gerson, acronym Ralbag). Indeed, his major philosophical work, Sefer Milhamot Ha-Shem (The War of the Lord, 1329), was called “Wars against the Lord” by one of his opponents. Despite the vilification of his position, Gersonides emerges as one of the most significant and comprehensive thinkers in the medieval Jewish tradition. He has been constantly quoted (even if only to be criticized), and, through the works of Hasdai Crescas and others, Gersonides’ ideas have influenced such thinkers as Gottfried Wilhelm Leibniz and Benedict de Spinoza. This article will survey his major contributions to medieval philosophy.