Thomas Aquinas's famous five arguments for God's existence, or 'Five Ways,' in Summa theologiae Ia q.2 a.3 are a cornerstone of thought and discussion about God and are still much debated today. In this book Peter Weigel provides the philosophical background, particularly surrounding Aquinas's metaphysics and theory of causation, needed to understand the Five Ways and examines the thinking behind the premises of these often difficult arguments. Weigel also considers larger issues surrounding arguing for God's existence beyond Aquinas's views, including more recent philosophical and scientific developments. He introduces readers to a wide array of thinkers and positions on the issues surrounding arguments for God, considers objections and other views from numerous historical and contemporary sources, and contemplates how Aquinas might respond to them. Written in clear prose with full explanations of technical concepts, his book will benefit a wide range of readers from undergraduates to advanced scholars.