Contextualization involves weaving together an interpretation of a document that situates it within its historical context. This study explores how undergraduate students approached the complex cognitive task of contextualizing historical documents. As part of their professional preparation to teach secondary social studies, undergraduate teacher candidates (TCs) conducted Decoding interviews with undergraduate students enrolled in world history and United States history survey courses. During these Decoding interviews--metacognitive interviews that surface and make explicit tacit thinking--TCs asked students to contextualize historical documents in order to elicit their cognitive processes. This case study presents findings from those interviews, uncovering a range of strategies that students used to contextualize documents, as well as a catalog of potential bottlenecks that hindered more expert contextualized thinking.