One of the most prominent thinkers of his generation, Hans Jonas wrote on topics as diverse as the philosophy of biology, ethics, social philosophy, cosmology, and Jewish theology -- always with a view to understanding morality as the root of our moral responsibility to safeguard humanity's future. A classic of phenomenology and existentialism and arguably Jonas's greatest work, The Phenomenon of Life sets forth a systematic and comprehensive philosophy -- an existential interpretation of biological facts laid out in support of Jonas's claim that mind is prefigured throughout organic existence.At the center of this philosophy is an attack on the fundamental assumptions underlying modern philosophy since Descartes, primarily dualism. Dissenting from the dualistic view of value as a human projection onto nature, Jonas's critique affirms the classical view that being harbors the good. In a brilliant synthesis of the ancient and modern, Jonas draws upon existential philosophy to justify core insights of the classical tradition. This critique transcends the historical limits of its phenomenological methodology and existential ethical stance to take its place among the most scientifically nuanced contemporary accounts of moral nature. It lays the foundation for an ethic of responsibility grounded in an assignment by Being to protect the natural environment that has allowed us to spring from it.