Reading comprehension is multidimensional and complex. The persistent challenges children, adolescents, and even adults face with reading comprehension call for concerted efforts to develop assessments that help identify sources of difficulties and to design instructional approaches to prevent or ameliorate these difficulties. Doing so requires drawing on extant research to understand the core components and processes of reading comprehension. This article reviews the theoretical and empirical literature on the construction of meaning during reading comprehension and derives implications for research, practice, and policy related to instruction and assessment. We focus specifically on the inferential processes that extract meaning from text and the sources of knowledge that facilitate the extraction and construction of meaning.