Six decades of studies on healthcare quality have persisted in rendering the subject difficult to understand or explain to health researchers and policymakers. This article advances three hypotheses about why quality in healthcare is such an enigma. The first concerns problems with the conceptualization of quality. Issues of uncertainty embedded in quality are discussed in the second hypothesis. Finally, difficulties in understanding quality are discussed within a model offered by the sociology of deviance. The article highlights the contribution of each hypothesis and integrates them into a plausible explanatory framework for quality's elusive compre-hensibility.