Hans Jonas was a well-known Jewish thinker, an early and influential biomedical ethicist, and an equally early and influential philosopher of technology in the United States and his native Germany. Born in 1904 in Monchengladbach, Jonas studied under Martin Heidegger at the University of Freiburg before Hitler came to power and Heidegger became chancellor of the university. He received his doctorate in 1928 from the University of Marburg. In 1933 he fled Germany and, in 1964, publicly repudiated Heidegger because of his Nazi connections. Jonas taught in Jerusalem and Canada before becoming a professor at the New School for Social Research in New York in 1955, where he was chair of the philosophy department (1957--63) and Johnson Professor of Philosophy (from 1966 until his retirement in 1976). Jonas is best known for his neo-Kantian ethics of responsible caution in the face of the awesome power of modern technology---especially the power of modern biotechnology, including genetic engineering. According to Jonas, we must consult our fears and not our hopes when understanding technological ventures that can have a potentially devastating impact on what it means to be human (and therefore ethical). More than half of Jonas's books were written in German, including an early version of his greatest work, The Imperative of Responsibility (1984).