This chapter delves into Jonas’s “principle of responsibility,” drawing on both published and unpublished material to examine its foundations. It explores the core elements of Jonas’s planetary ethic, including his theory of duties based on the imperative of responsibility, the role of the “heuristics of fear,” the importance of nature, and his critique of utopia. This ethical framework stands apart from positivist or analytical philosophical currents, as Jonas seeks to establish an ethic suited to the age of technology—one that metaphysically applies to human action within the natural world. The chapter illustrates how Jonas’s argument is built on two key principles: the self-assertion of being over non-being, and the ontological axiom of the superiority of purpose over purposelessness.