Meditation on the work of Martin Heidegger reveals unambiguously that this philosopher's thought is centred on being as Open. This observation cannot fail to raise questions about the possibility of a fundamental anthropology inspired by fundamental ontology and whose aim is to remedy the inadequacy of ancient and Christian anthropology denounced by Heidegger in his main work Sein und Zeit (Being and Time). What is the truth of man? This is the essential question that this book attempts to answer. Heidegger, starting from the question "what is being?" implicitly contained in the guiding question "why is there being and not rather nothing?", aims no less at the truth of man, insofar as it is in the openness of being that fundamental anthropology reaches its full meaning.