In an academic setting, sources of information that can help the author answer a question or make sense of a problem are judged on competence and trustworthiness. As she locates a written text, an image, or a person, and "interrogate" it, the author is working through a series of judgment calls that end in a summative assessment of credibility. That final, overall assessment is an iterative process and is based on three factors: (1) definition of credibility; (2) specific attributes of the source; and (3) application of rules of thumb that have worked in the past to identify credible information. In this article, the author discusses how to evaluate the trustworthiness of information and how to teach evaluation as inquiry. (Contains 7 figures and 1 footnote.)