During the fifteenth century, the Scientific Revolution signaled a major shift in the way people viewed the natural world. Today, Rene Descartes is perhaps best known as the father of modern Western philosophy, but he also played an important role in the development of a rational approach toward scientific questions. He was a gifted mathematician and his examinations of the natural world led him to develop theories about light, the formation of the universe, and how the human mind works. This biography shows how Descartes’s rational method inspired his own discoveries and continues to resonate today.