In this article, we argue that teachers' epistemic cognition, in particular their thinking about epistemic aims and reliable processes for achieving those aims, may impact students' understanding of complex, controversial issues. This is because teachers' epistemic cognition may facilitate or constrain their implementation of instruction aiming to engage students in reasoned argumentation through classroom dialogue. We also suggest that teachers may need to reflect on their own epistemic cognition in the context of dialogue-based instruction in order to calibrate it with the aim of deep understanding and the reliable process of reasoned argumentation, which underlie such instruction. Based on our discussion of relevant theoretical frameworks and related empirical evidence, we identify several promising directions for future theoretical and empirical work in this area. In a unique way, this article brings together theoretical frameworks and bodies of empirical work that hitherto have been discussed separately to provide new insights into the potential relationship between teachers' epistemic cognition and students' understanding.