Drawing on the theory of documents representation (Perfetti et al., Toward a theory of documents representation. In: H. v. Oostendorp & S. R. Goldman (Eds.), "The construction of mental representations during reading." Mahwah, NJ: Erlbaum, 1999), we argue that successfully dealing with multiple documents on the World Wide Web requires readers to form documents models; that is, to form a representation of contents "and" sources. We present a study in which we tested the assumption that the use of metacognitive strategies is crucial to the formation of documents models. A total of 100 participants with little medical knowledge were asked to conduct an Internet research on a medical topic. Participants were randomly assigned to four experimental groups that received different types of metacognitive prompts: participants either received evaluation prompts, monitoring prompts, both types of prompts, or no prompts. A control group took paper-and-pencil notes. Results showed that laypersons receiving evaluation prompts outperformed controls in terms of knowledge about sources and produced more arguments relating to the source of information when justifying credibility judgments. However, laypersons receiving evaluation prompts were not better able to indicate the source of information after Internet research than controls. In addition, laypersons receiving monitoring prompts acquired significantly more knowledge about facts, and performed slightly better on a comprehension test. It is concluded that the results underline the importance of metacognition in dealing with multiple documents.