The notion of a law of nature is central for our enterprise. First, one of the readings of the microphysicalists’ thesis concerns laws of nature explicitly. Second, micro-explanation as analysed in the next chapter is essentially the explanation of laws that pertain to compounds in terms of laws that pertain to constituents. The main argument of the following chapters does not depend on any particular view on laws of nature. All that I need is the distinction between constants, states and laws of nature. However, in Chapters 6 and 7 I will make use of a feature of laws of nature that is not yet generally acknowledged. Laws of nature can be explanatory even though they are not instantiated, i.e. even though the behaviour they describe is not (completely) manifest. This feature has been accommodated by dispositionalist theories of laws of nature. I will now sketch such an account.