Hans Jonas (1903-1993) was one of the most creative and original Jewish thinkers of the twentieth-century. This volume offers a retrospective of Jonas's life and works by bringing together historians of modern Germany, Judaica scholars, philosophers, bioethicists, and environmentalists to reflect on the meaning of his legacy today. From a historian of religions, who wrote a path-breaking monograph on Gnosticism, Jonas turned to the philosophy of nature, extending his existential philosophy and phenomenological analysis to include all forms of life. Unique among twentieth-century Jewish philosophers, Jonas argued for the possibility of a genuinely symbiotic relationship between humanity and nature, which he believed had been suppressed by modern technology. Jonas spoke against the human domination of nature on the basis of Jewish sources, especially the Bible and Lurianic Kabbalah, and he was among the first to define the ethical challenges that modern technology poses to humanity.