When an agent “loses herself” in a project, or becomes completely absorbed in an activity, she has what Heidegger calls “reflected self-understanding”. This kind of reflected understanding allows the agent to find herself out in the world, “in things”, without ever holding any reflexive attitudes about herself. In my dissertation, I develop and defend Heidegger’s account of reflected self-understanding, which constitutes – for Heidegger – the most basic grip an agent has on who she is. I suggest that Heidegger’s account of reflected self-understanding is not only a significant contribution to the history of philosophy, but also the central kernel that structures Heidegger’s thought on the topics of understanding, interpretation, truth, and authenticity in Being and Time.