Prior knowledge is one of the strongest contributors to comprehension, but there is little specificity about different aspects of prior knowledge and how they impact comprehension. This article introduces the Multidimensional Knowledge in Text Comprehension framework, which conceptualizes prior knowledge along four intersecting dimensions: amount, accuracy, specificity, and coherence. "Amount" refers to how many relevant concepts the reader knows. "Accuracy" refers to the extent to which the reader's knowledge is correct. "Specificity" refers the degree to which the knowledge is related to information in the target text. "Coherence" refers to the interconnectedness of prior knowledge. Conceptualizing prior content knowledge along these dimensions deepens understanding of the construct and lends to more specific predictions about how learners process information. Considering knowledge across multiple dimensions is crucially important to the development and selection of prior knowledge assessments and, in turn, educators' ability to capitalize on learners' strengths across various comprehension tasks. [For the corresponding grantee submission, see ED616077.]