Authenticity is often touted as an important virtue for teachers. But what do we mean when we say that a teacher ought to be "authentic"? Research shows that discussions of teacher authenticity frequently refer to other character traits or simply to teacher effectiveness, but authenticity is a unique concept with a long philosophical history. Once we understand authenticity as an ethical and metaphysical question, the presumed connection between authenticity and teaching appears less solid. While being true to oneself may render it more likely that a teacher does her job well, there is also reason to believe that excellent teachers can be inauthentic and that inept or even very dangerous teachers can be authentic. This paper breaks down the concept of teacher authenticity and examines three cases to show that the relationship between authenticity and good teaching is less direct that it may initially seem.