In this early lecture series, the author of Being and Time develops his unique approach to understanding humanity’s relationship to the world. This volume presents a collection of Martin Heidegger’s lectures delivered at the University of Freiburg in the winter of 1921–1922. Preceding Being and Time, the work shows the young Heidegger introducing novel vocabulary as he searches for his genuine philosophical voice. In this course, Heidegger first takes up the role of the definition of philosophy and then elaborates a unique analysis of “factical life,” or human life as it is lived concretely in relation to the world, a relation he calls “caring.” Heidegger’s descriptions of the movement of life are original and striking. As he works out a phenomenology of factical life, Heidegger lays the groundwork for a phenomenological interpretation of Aristotle, whose influence on Heidegger’s philosophy was pivotal.