Recently, it has been proposed that schools teach disciplinary literacy in science, mathematics, history, and literature classes as students move into middle school and high school. A disciplinary literacy approach emphasizes the specialized knowledge and abilities possessed by those who create, communicate, and use knowledge within each of the disciplines. This article compares disciplinary literacy with the more widely emphasized approach known as content area literacy and provides an analysis of the growing research base underlying the disciplinary literacy construct. Research studies on disciplinary literacy are drawn from expert–novice comparisons in which think-aloud data are collected, during reading, from experts (i.e., mathematicians, chemists, historians) and students, and from functional linguistics analyses of the features of the grammars in disciplinary texts to identify the purposes and cognitive and communicative approaches that these grammars reveal. Finally, implications for school programs and instruction are considered.