Many journal articles detail recommendations to naturally integrate literacy instruction into content-area classes, particularly science, claiming that such instructional practices will support both literacy and content-knowledge acquisition. This begs the question, are the literacy strategies recommended for content-area instruction founded in established educational theories? The purpose of the current study is to examine the implicit and explicit theories driving science disciplinary literacy instruction. Theories assist in organizing and advancing research in a systematic manner. Information on the status of theory is essential to both practitioners (who are implementing strategies) and researchers (who are making recommendations for classroom instruction). Our study revealed that in science literacy, vocabulary instructional practices are frequently supported with Schema and Dual-Coding theories. Articles also frequently used theories grounded in social dynamics, including social constructionism and sociocultural perspective, to support literacy instruction. However, recommendations for other aspects of instructional practices in science literacy are generally not well-grounded in major reading theories.