The prevailing assumption by some that deep processing promotes stronger learning outcomes while surface processing promotes weaker learning outcomes has been called into question by the inconsistency and ambiguity of results in investigations of the relation between levels of processing and performance. The purpose of this literature review is to examine four areas that may be contributing to the inconsistency and ambiguity of these research results: conceptualization, operationalization, situational factors, and model specification of deep and surface processing. A PsycINFO database search was conducted, and 221 studies were identified for a comprehensive data table. Analysis of these data revealed trends that suggested conceptualization and operationalization of deep and surface processing differed depending on the theoretical frame utilized in each study. Additionally, the choice of theoretical frame also seemed to impact what situational factors may or may not have been present as well as how the model of levels of processing and performance was specified. Results from studies that met certain criteria demonstrated that levels of processing and performance are related, and further, these relations may be moderated by other factors. Implications for future research are discussed that focus on these four areas. (Contains 3 tables and 7 figures.)