At the very outset and up to the end, the long philosophical journey of Martin Heidegger (1889-1976) remained oriented by a single question, the question of Being, the Seinsfrage. This does not mean, however, that the question preserved the same meaning or ruled an identical field of investigation throughout the whole journey. Indeed, Heidegger himself repeatedly claimed that at some point a turn (Kehre) occurred in his thought. Moreover, thanks to the current publication of his entire corpus (Gesamtausgabe), it is now possible to draw a fair picture of the vicissitudes of the journey. For the purpose of this chapter, I propose to divide Heidegger's work into two phases. The first covers publications and lecture courses devoted to setting out the project of what Heidegger, at that time, called 'fundamental ontology'. The later phase covers writings which are all characterized by a meditation on the history of Being. Whereas the project of fundamental ontology aimed at completing metaphysics as the science of Being, the later meditation consistently aimed at overcoming metaphysics .