It is widely accepted that the ethical supervenes on the natural, where this is roughly the claim that it is impossible for two circumstances to be identical in all natural respects, but different in their ethical respects. This chapter refines and defends the traditional thought that this fact poses a significant challenge to ethical non-naturalism, a view on which ethical properties are fundamentally different in kind from natural properties. The challenge can be encapsulated in three core claims which the chapter defends: that a defensible non-naturalism is committed to the supervenience of the ethical, that this commits the non-naturalist to a brute necessary connection between properties of distinct kinds, and that commitment to such brute connections counts against the non-naturalist’s view. Each of these claims has recently been challenged. Against Nicholas Sturgeon’s recent doubts about the dialectical force of supervenience, this chapter defends a supervenience thesis as deserving to be common ground among ethical realists. It is then argued that attempts to explain supervenience on behalf of the non-naturalist either fail as explanations, generate near-identical explanatory burdens elsewhere, or appeal to commitments that are inconsistent with core motivations for non-naturalism. The chapter concludes that, suitably refined, the traditional argument against nonnaturalism from supervenience is alive and well.