The prevailing narrative in the history of science maintains that the ancient Greeks did not have a concept of a ‘law of nature’. This paper overturns that narrative and shows that some ancient Greek philosophers did have an idea of laws of nature and, moreover, they referred to them as ‘laws of nature’. This paper analyzes specific examples of laws of nature in texts by Plato, Aristotle, Philo of Alexandria, Nicomachus of Gerasa, and Galen. These examples emerged out of the (...) closely intertwined Platonic and Pythagorean traditions, and these philosophers’ texts make reference to laws of nature when describing arithmetical methods, arithmological doctrines, or medical theories. Nicomachus’ laws of nature are especially noteworthy, because they have features that historians look for in the search for the origin of the modern concept of laws of nature. Nicomachus’ laws of nature are mathematical, universal, and necessary. This paper raises the possibility that the ancient Platonic and Pythagorean traditions influenced the subsequent development of the idea of laws of nature in medieval and early modern Europe, including the conception of laws of nature deployed by Johannes Kepler and Isaac Newton. (shrink)