Abstract The goal of this article is to analyze the role of convention in interpreting physical theories—in particular, how the distinction between the conventional and the nonconventional interacts with judgments of equivalence. We will begin with a discussion of what, if anything, distinguishes those statements of a theory that might be dubbed “conventions.” This will lead us to consider the conventions that are not themselves part of a theory’s content but are rather applied to the theory in interpreting it. Finally, we will consider the idea that what conventions to adopt might, itself, be regarded as a matter of convention.