Being and Time by Martin Heidegger.

The primary philosophical problem for Martin Heidegger is the problem of Being. His major philosophical treatise, Being and Time, constitutes an attempt at a formulation of the basic questions and forms of analysis that are to lead to a clarification of the meaning and structures of Being. The form of analysis that peculiarly characterizes Being and Time is what Heidegger calls Daseinsanalytik (analysis of human being). This form of analysis is adopted because it is believed that humankind is the portal to the deeper levels of reality and that only through a disciplined analysis and description of human being can the path be opened for an apprehension of Being itself.