My dissertation lays out some of the chief philosophical precursors to Jonathan Israel’s Radical Enlightenment. It investigates the principal question of Will Durant’s The Age of Voltaire: “How did it come about that a major part of the educated classes in Europe and America has lost faith in the theology that for fifteen centuries gave supernatural sanctions and supports to the precarious and uncongenial moral code upon which Western civilization has been based?” The aim of this project is both broad and specific: the first is to provide a general history of the philosophical precursors to the Radical Enlightenment up until the early modern period, and the second is to highlight one of these precursors in detail, which I do in the large Spinoza part. With the assistance of a great deal of scholarship in philosophy of religion, history of philosophy, theological analysis, biblical criticism, and historiography, my dissertation contends that the major philosophical precursors against orthodox faith in revelation and for the Radical Enlightenment have been derived primarily from several forces. I present some of the general arguments of some of the pre-Socratics and Greek philosophers, especially Socrates and Plato, emphasizing their rationalist and non-theological thinking. Then I point out how some of this Greek philosophical literature led to new philosophical and theological elements in some of the teachings of the Church Fathers, some of the medievals, and some of the scholastics, up to the early modern period. The core of my argument, however, begins to pick up steam at the Renaissance. With the Renaissance, the Scientific Revolution, and the early Enlightenment New Philosophy, everything changes. Renaissance textual criticism of ancient texts leads to the beginnings of some genuine biblical criticism. The explosion of naturalist-leaning explanations of nature via Copernicus, Galileo, Descartes and many others in the Scientific Revolution leads many to wonder if God is needed. The rejection of Aristotelian and Scholastic metaphysics by the New Philosophers, most notably, Descartes, undermine what for many provided the philosophical underpinnings for the Church and theology. And then “the most unkindest cut of all,” the revolutionary historical and textual criticism of the Bible (by many early Enlightenment philosophers, especially Spinoza) which utterly undermines and refutes Judaism and Christianity.