In this chapter, I build a theory of explanatory understanding using Evidentialism as my epistemology. This may not initially seem like a promising endeavor for two reasons. First, Evidentialism is a theory of knowledge which entails a propositional account of understanding, and many philosophers think understanding is quite different from knowledge. For instance, as Jonathan Kvanvig points out, what comes to mind when we think about knowledge are issues about evidence, reliability, reasons for belief, and anti-luck conditions; whereas when we think about understanding, it is our grasp of logical, probabilistic, or explanatory relationships that come to mind (Kvanvig 2009, 97). There is surely something right in this. For instance, understanding a theory like classical mechanics requires the appreciation of a host of structural relationships (mostly between equations) which allow one to solve physics problems, and this seems to go far beyond merely knowing what the theory says. Second, Evidentialism, at least in its most popular form, appeals to an explicit explanatory decision-making process: inference to the best explanation (IBE). But IBE has serious problems of its own. Perhaps the most serious criticisms have come in the form of underdetermination arguments, suggesting there are always alternative explanations from those we consider the best, no matter how compelling our evidence. To the extent that Evidentialism adopts IBE it may be subject to similar attacks.