 Following R. M. Hare (1952), claims of such general necessary connection are called ethical supervenience theses. Such theses have played a key role in arguments for and against a variety of influential views about ethics. This entry aims to introduce the idea of ethical supervenience and its philosophical significance. The entry considers ways of making more precise the claim that the ethical supervenes, and what case can be made for the supervenience of the ethical. It then considers arguments that use ethical supervenience as a premise, and doubts that ethical supervenience has the sort of significance suggested by these arguments.