Like its predecessor, New Dimensions in Bioethics, this volume developed out of a series of lectures at Yale University's Institution for Social and Policy Studies. Each speaker in the Bioethics and Public Policy Seminar Series was invited because of their expertise in a given area of bioethics. Each of the more successful participants was invited to contribute a manuscript for publication. The essays are bound together by the application of ethical analysis to scientific questions and by consideration of policy implications. At its inception, bioethics was virtually synonymous with medical ethics. As the field grew and attracted new practitioners, it became clear that other applications of this new subject required an extension of its scope. For example, environmental ethics, propelled by authors such as Aldo Leopold and Rachel Carson, quickly developed a vigorous literature of its own.