I argue that there are at least two concepts of law of nature worthy of philosophical interest: strong law and weak law. Strong laws are the laws investigated by fundamental physics, while weak laws feature prominently in the “special sciences” and in a variety of non-scientific contexts. In the first section, I clarify my methodology, which has to do with arguing about concepts. In the next section, I offer a detailed description of strong laws, which I claim satisfy four criteria: (...) (1) If it is a strong law that L then it also true that L; (2) strong laws would continue to be true, were the world to be different in some physically possible way; (3) strong laws do not depend on context or human interest; (4) strong laws feature in scientific explanations but cannot be scientifically explained. I then spell out some philosophical consequences: (1) is incompatible with Cartwright’s contention that “laws lie” (2) with Lewis’s “best-system” account of laws, and (3) with contextualism about laws. In the final section, I argue that weak laws are distinguished by (approximately) meeting some but not all of these criteria. I provide a preliminary account of the scientific value of weak laws, and argue that they cannot plausibly be understood as ceteris paribus laws. (shrink)