Increasing calls for greater STEM-integrated experiences in K–12 education have spawned numerous studies on teacher beliefs, educational goals, and practices for teaching and learning. However, how the field proposes to support the development of teachers’ STEM-integrated disciplinary knowledge appears to be underresearched. In this systematic review, we analyzed 110 articles to determine (a) in what ways has the literature focused on teacher learning, (b) to what extent the literature addressed the development of teachers’ STEM-integrated disciplinary knowledge, and (c) to what extent the literature identified mechanisms for developing teachers’ STEM-integrated disciplinary knowledge. Results reveal needs that include, among others, more studies focused on developing teacher disciplinary knowledge; studies that differentiate teacher needs at different grade levels; studies that differentiate mechanisms aimed at developing teachers’ pedagogical knowledge, pedagogical content knowledge, and disciplinary knowledge; and studies that explicitly examine the mechanisms being used to support the development of teachers’ STEM-integrated disciplinary knowledge.