This article addresses the perennial issue of the criteria by which qualitative research should be evaluated. At the present time, there is a sharp conflict between demands for explicit criteria, for example in order to serve systematic reviewing and evidence-based practice, and arguments on the part of some qualitative researchers that such criteria are neither necessary nor desirable. At issue here, in part, is what the term "criterion" means, and what role criteria could play in the context of qualitative enquiry. Equally important, though, is the question of whether a single set of criteria is possible across qualitative research, given the fundamental areas of disagreement within it. These reflect divergent paradigms framed by value assumptions about what is and is not worth investigation. In addition, there are differences in methodological orientation: over what counts as rigorous enquiry, realism versus constructionism, and whether the goal of research is to produce knowledge or to serve other goals. (Contains 21 notes.)