<p>Metacognitive regulation can help students coordinate and direct their progress toward achieving their epistemic aims as they make sense of multiple documents. However, little is known about how learners engage in social regulation of epistemic thinking during collaborative inquiry with multiple documents. Hence, the purpose of this study was to identify and characterize how students engage in self-, co-, and shared metacognitive regulation of epistemic aims, ideals, and reliable processes during collaborative document-based inquiry. We also examined whether and how the regulation of epistemic thinking changes over time. The participants included two dyads of ninth-grade students who met over twelve sessions to engage in facilitated collaborative inquiry. Students engaged in four biology units that included multiple documents that made conflicting claims and had diverse credibility. We coded students’ discourse to identify epistemic aims, ideals, and reliable processes for making sense of the documents and how they regulated these components. Students frequently articulated regulation of their epistemic thinking, with epistemic aims being the most frequently regulated component. Students engaged in self-, co-, and shared regulation of their aims, ideals, and processes, articulating shared regulation most often. Over time, there appeared to be a gradual increase in social regulation of epistemic thinking (shared and co-regulation) and a rise in regulation of epistemic ideals. The findings highlight the central role of social regulation of epistemic thinking in document-based inquiry. They also suggest that social regulation, particularly of epistemic ideals, might expand over extended inquiry. These findings underscore the importance of incorporating social regulation in models of multiple document literacy and epistemic thinking.</p>