As scholars and their audiences pursue standards of evidence, standards for literature reviews have also become salient. Many authors advocate "systematic" reviews and articulate standards for these. This article compares the bodies of literature derived from systematic and other types of review, which the author labels conceptual, and examines problems associated with different approaches to defining a body of literature. These problems include (a) defining the boundaries of the literature, (b) distinguishing studies from citations, (c) distinguishing literature from lore, (d) deciding which reporting venues to include, and (e) weeding out anomalous studies. The article demonstrates that although systematic reviews may remove some biases through their inclusion rules, they may introduce other biases through their exclusion decisions and may thwart conceptual advances in a field. (Contains 4 tables.)