This dissertation describes the credibility judgment process using social psychological theories of dual-processing, which state that information processing outcomes are the result of an interaction “between a fast, associative information- processing mode based on low-effort heuristics, and a slow, rule-based information processing mode based on high-effort systematic reasoning” (Chaiken & Trope, 1999, p. ix). Further, this interaction is illustrated by describing credibility judgments as a choice between examining easily identified peripheral cues (the messenger) and content (the message), leading to different evaluations in different settings. The focus here is on the domain of the Web, where ambiguous authorship, peer- produced content, and the lack of gatekeepers create an environment where credibility judgments are a necessary routine in triaging information. It reviews the relevant literature on existing credibility frameworks and the component factors that affect credibility judgments. The online encyclopedia (instantiated as Wikipedia and Encyclopedia Britannica) is then proposed as a canonical form to examine the credibility judgment process. The two main claims advanced here are (1) that information sources are composed of both message (the content) and messenger (the way the message is delivered), and that the messenger impacts perceived credibility; and (2) that perceived credibility is tempered by information need (individual engagement). These claims were framed by the models proposed by Wathen & Burkell (2002) and Chaiken (1980) to forward a composite dual process theory of credibility judgments, which was tested by two experimental studies. The independent variables of interest were: media format (print or electronic); reputation of source (Wikipedia or Britannica); and the participant’s individual involvement in the research task (high or low). The results of these studies encourage a more nuanced understanding of the credibility judgment process by framing it as a dual-process model, and showing that certain mediating variables can affect the relative use of low-effort evaluation and high- effort reasoning when forming a perception of credibility. Finally, the results support the importance of messenger effects on perceived credibility, implying that credibility judgments, especially in the online environment, and especially in cases of low individual engagement, are based on peripheral cues rather than an informed evaluation of content. / text