Platonists in the philosophy of mathematics believe that mathematical beliefs posit objects that are mind- and language-independent, causally inert, and exist beyond time and space. The Benacerraf challenge concerns how to reconcile that belief with the existence of mathematical knowledge. This chapter explores whether the Benacerraf challenge really does provide the critics of non-naturalist moral realism with the extra resources. Accordingly, insofar as the advocates of the Benacerraf-argument do not want their position to collapse into some sort of global skepticism, the circularity that is involved by Enoch's strategy should be deemed legitimate. Benacerraf's own version is widely seen as unsatisfying, however, because he explicitly presupposes a causal theory of knowledge whose plausibility can be questioned on independent grounds. The chapter focus on the more recent version that is due to Hartry Field. Field takes the challenge to concern the "reliability" of the mathematical beliefs.