This chapter examines learning from multiple documents, that is, the construction of new knowledge, beliefs or opinions from more than a single source of information. First, we introduce the specific discourse processes that come into play when multiple-source documents are considered, as opposed to single-source texts or multimedia documents. We focus on the definition and role of sources, as well as on the semantic and rhetorical relationships at an intertextual level. Then we examine learning from multiple documents from a cognitive standpoint. We define two core principles: the sourcing principle and the multiple-document integration principle. Finally, we examine some implications of these principles for a general theory of text-based learning and for instructional practice throughout primary, secondary and higher education curricula.