What happens when we move from knowing that something is the case to understanding why it is the case: e.g., from knowing that the eclipse occurred to understanding why it occurred? According to a long line of philosophers, the move from knowing that to understanding why is not the result of acquiring some sort of superknowledge but is rather simply the result of acquiring more knowledge: in particular, it is said, it is the result of acquiring a knowledge of causes. Although this is the traditional view of understanding, several recent philosophers have argued that it can no longer be sustained. According to Duncan Pritchard, Jonathan Kvanvig, and Catherine Elgin, for example, knowledge of causes is either not necessary for understanding, or not sufficient, or both. In this paper I consider some of the objections that have been made to the traditional view, and argue that what they show is not that the traditional view is mistaken, but rather that it needs to be understood in a particular way. More specifically, I argue that what the objections show is that the primary object of understanding is not a proposition or set of propositions, but rather the actual causal relationships (or, more broadly, modal relationships) that obtain in the world.