Heidegger's primary concern in Being and Time is the question of the meaning of being—a distinctly ontological concern. Yet, with discussions of death, guilt, conscience, anxiety, uncanniness, authenticity, and inauthenticity, Heidegger seems to end up in existential territory. The ontological import of these existential excursions is difficult to discern—indeed, it has not been identified in leading interpretations. In this paper, I aim to highlight the ontological import of Heidegger's analysis of anxiety—it manifests the inadequacy of Dasein's fallen and inauthentic self-understanding, (...) which is motivated by the inadequacy of Dasein's fallen and inauthentic, average understanding of being. In making this case, I will clarify the sense in which anxiety involves an experience of world-collapse and show how it functions to reveal the possibilities of authenticity and inauthenticity. (shrink)