We frequently speak of certain things or phenomena being built out of or based in others. This soda can is made of molecules, which are in turn made of atoms, which are in turn made of subatomic particles. The behavior of a crowd is based in the behaviors of and interactions between individual people—it behaves as it does in virtue of the individual behaviors and interactions. Making Things Up concerns the family of relations that such talk appeals to, which Karen Bennett calls “building relations.” Grounding is one currently popular such relation; so too are composition, property realization, and—controversially—causation. Building relations connect more fundamental things (like atoms) to less fundamental things (like soda cans). But what are we even talking about when we say that something is more fundamental than something else? This book illuminates the ideas of building and fundamentality, as they are deployed in metaphysics and elsewhere in philosophy. Bennett paints a picture of a hierarchically structured world, and makes good sense of otherwise somewhat cryptic talk of “in virtue of” and fundamentality.