The overarching question in this chapter is, what makes this theory—indeed, any theory—a theory of justice? Five criteria prominently discussed in the literature—special importance, stringency, claimability, specificity, and rightful enforceability—are examined. The position defended in this book is developed with respect to each criterion. In addition, two norms of structural unfairness pertaining to differentials of power and advantage are distinguished, as are the ways in which each differs from human rights norms. We look first at the ordinary language used in situations of everyday experience. We then extrapolate from basic intuitions about relatively simple patterns of unfairness in interpersonal relationships to gain a better understanding of fairness norms, applicable in more complex contexts where an array of institutions and social practices structure relationships between social groups.