The philosophy of science-the attempt to understand the fundamentals of one of the most significant of human activities-has traditionally treated itself as a branch of the field of epistemology. Justification for this delimitation has relied on two distinctions. One is the difference between the contexts of discovery and of justification. The process of scientific discovery is viewed as a mysterious, non-rational process belonging to the province of psychology. In response, the philosophy of science limited itself to probing the logical procedures of justifying scientific claims. second is the distinction between externalist and internalist features of science. The philosophy of science sets aside the external economic or political factors promoting scientific work in order to focus on those processes internal to scientific research. In recent decades, however, these assumptions have faced two challenges. One challenge originated with arguments for the close, even symbiotic relationship between science and technology, and as a response to the external social problems of technology, from nuclear weapons to biotechnology. In consequence, the philosophy of technology developed as a complement to the philosophy of science, with a particular focus on ethicalpolitical criticism. A second challenge originated with historical and sociological studies of science that revealed important nonepistemological features of its internal processes. Of special importance here are the ethical dimensions of scientific methods, with discussions of the professional ethics of science, and accounts of the material culture of science, where the scientific method is placed within the larger framework of scientific tools, public and private institutions, and governmental funding streams. Bridging the external social impacts of scientific activity and its internal social construction is the less well known but no less important activity of science policy. Science policies are manifest both outside science in public appropriations for the funding of science and regulatory legislation, and inside science with efforts to refine the procedures of peer review or promote the more effective and equitable sharing of data and peer review. Original recognition and analysis of these activities belongs to the social sciences, and to research undertaken by that interdisciplinary field known as science, technology, and society studies. As guest editors of this special issue of Philosophy Today, however, our goal is to promote the emergence-after the philosophy of technology and the professional ethics of science-of a third complement to traditional philosophy of science that focuses on this under-appreciated bridge. Philosophical reflection on science policy will expand our understanding of science, extend the activity of philosophy, and strengthen our grasp of the controversies facing policy professionals. Philosophy of Science Absent Policy To repeat: Complementing science is another, no less significant activity, that of science policy-which is itself simply one aspect of what has been called the "policy orientation" (Lerner and Lasswell, eds., 1951) and the "policy movement" (Brunner, 1991) that promotes the development of systematic, intelligent, and effective public decision making. In a distinction that goes back at least to Harvey Brooks (1968)-and which is not precisely the same as that between external and internal science policy-science policy is commonly divided into "policy for science" and "science for policy." In either case, science policy is distinct from science, in that it attempts to investigate, formulate, and implement guidelines for science-society relationships, so that society promotes the steady advancement of science (policy for science) and science benefits public decision making (science for policy). Like science itself, science policy is thus of considerable societal importance. Remarkably, however, although there exist efforts to advance science policy work itself and to examine it from the perspectives of science, technology, and society studies, there is little in the way of a research program in philosophy attempting to analyze and understand science policy more generally, either in its epistemological or its ethical dimensions. …