My dissertation is divided into three self-contained chapters, each of which explores some facet of nominalism. The overall aim is to explicate and defend a nominalist approach that recognizes the utility of talking about, or presupposing the existence of, abstract objects even if no such objects exist. The first chapter begins with a question: why is talk about abstract mathematical entities so useful in describing and explaining the physical world? Here is an answer: talk about such entities is useful for describing and explaining the physical world insofar as there is some appropriate structural similarity between them and the target physical system. But this account leads to a problem: there is no guarantee that the world contains a suf...