Despite the importance of source attention and evaluation for learning from texts, little is known about the particular conditions that encourage sourcing during reading. In this article, basic assumptions of the discrepancy-induced source comprehension (D-ISC) model are presented, which describes the moment-by-moment cognitive processes that readers undergo when reading-to-understand controversial messages. We then review supporting evidence from single and multiple text comprehension research. In the discussion, we draw conclusions based on the theoretical and empirical research, highlight limitations of what is known to date, and suggest how further investigations of D-ISC might address these concerns.