This volume contains the complete publication of the Bremen lecture series "Insight into What Is" (1949) and the Freiburg lecture series "Principles of Thinking" (1957). Both lecture series provided a broader audience with insight—albeit still limited—into the ontological thinking of late Heidegger at the time of their oral presentation and the subsequent, though only partial, publication. The Bremen lectures unfold under the title "Insight into What Is" by following the guiding question of the full essence of the thing and its preservation in the age of technology as the dominance of the framework, in which beings appear only in the form of an orderable stock. They address the essential question of the fundamental event of this ontological constellation and the hidden danger within it, as well as its possible overcoming.