This work is a publication of a manuscript left unfinished at his death by the author. From the time of their conversations in 1936, William Henry Werkmeister has studied the phenomenon of Martin Heidegger's thought and the critical literature commenting on it. During a period spanning 36 years, Werkmeister wrote some nine articles and reviews about his findings. He turned to other interests, but the Heidegger phenomenon continued to reside at the back of his mind. At age ninety, Werkmeister set out once again to write a work that would unify Heidegger's thought, clarify a number of its essential features, place Heidegger's chief works in an order that corresponds to the time line of his thought, critically appraise the development of his thought against the work of other German philosophers (particularly Nicolai Hartmann), and assess the question of Heidegger's alleged Nazi sympathies.