486Critical sociology of science, in conjunction with an emancipatory epistemology, focuses attention on the social and especially value aspects of validity and objectivity. This is the foundation for our arguments concerning the relevance of the sociology of science for explaining and understanding science, and for fashioning science policy. After outlining the basic features of critical sociology of science and emancipatory epistemology, we explore their implications for the problem of validity in applied social science research. Drawing on research on the use of illegal drugs, we argue that Campbell's suggestions regarding how to define research problems and treat qualitative methods, as well as other aspects of his "sociology of scientific validity, " may improve validity in the sense of achieving consensus and vigor within specialties. More generally, however, his program may inhibit progress in developing accurate, objective knowledge of science and society. Formal policy research is inevitably ideological; validity is enhanced by broadening the basis of research support, adopting the perspectives of a variety of communities, and resisting the temptation to enthrone particular methods or work styles.This article is at once a response and an alternative to Donald T. Campbell's (1985) program for a &dquo;sociology of scientific validity&dquo; and his proposals for optimizing validity in applied social science research.