Martin Heidegger's magnum opus, "Being and Time," delves into the fundamental question of Being, a concept he argues has been neglected by Western philosophy since the time of the ancient Greeks. Heidegger introduces the term "Dasein," which translates to "being-there" or "being-in-the-world," to reframe the way we understand existence. Unlike traditional philosophical notions that separate subject and object, Heidegger’s Dasein emphasizes the interconnectedness of the individual and the world. This essay explores Heidegger's concept of Dasein, its temporal development, the implications of being-toward-death, and the notions of thrownness, projection, care, and authenticity.