Basic Problems of Phenomenology presents the first English translation of Martin Heidegger's early lecture course from the Winter of 1919/1920, in which he attempts to clarify phenomenology by looking at the phenomenon of life, which he sees as the primary area of research for phenomenology. Heidegger investigates the notions of life and world, and in particular the self-world, Christianity, and science in an attempt to discern how phenomenology is the primordial science of life and how phenomenology can take account of the streaming character of life. Basic Problems of Phenomenology provides invaluable insights into the development of Heidegger's thoughts about human existence up to Being and Time. It also offers a compelling insight into the nature of the world and our ability to give an account of human life. As an account of Heidegger's early understanding of life, the text fills an important gap in the available literature and represents a crucial contribution to our understanding of the early Heidegger.