While the science and religion literature frequently refers to the laws of nature, the idea of law itself is typically left unanalyzed. This obscures an important conceptual change in the history of science. That nature contains regularities is not a modern discovery. But what is responsible for those regularities? For Plato it was the Forms. For Aristotle, it was essences and natures. While the idea of natural law had a long tradition in ethics, at least back to the Stoics, it took Descartes to unambiguously apply the idea to physics. This was no incremental change. The ramifications for divine freedom, empiricism, and special divine action are discussed.