This report is the final product of a two-year study by the Committee on Integrated STEM Education, a group of experts on diverse subjects under the auspices of the National Academy of Engineering (NAE) and the Board on Science Education of the National Research Council (NRC). The committee’s charge was to develop a research agenda for determining the approaches and conditions most likely to lead to positive outcomes of integrated STEM (science, technology, engineering, mathematics) education at the K–12 level in the United States. In fulfilling that charge, the committee identified and characterized existing approaches to integrated STEM education, in both formal and after-school and informal settings. It also reviewed the evidence for the impact of integrated approaches on various parameters of interest, such as greater student awareness, interest, motivation, and achievement in STEM subjects; improved college-readiness skills; and boosts in the number and quality of students who may consider a career in a STEM-related field. Over the past decade, the STEM acronym has developed wide currency in US education and policy circles. Leaders in business, government, and academia assert that education in the STEM subjects is vital not only to sustaining the innovation capacity of the United States but also as a foundation for successful employment, including but not limited to work in the STEM fields. Historically, US K–12 STEM education has focused on the individual subjects, particularly science and mathematics. Reform efforts, including development of learning standards and, more recently, large-scale assessments, likewise have treated the STEM subjects mostly in isolation. The relatively recent introduction of engineering education into some K–12 classrooms and out-of-school settings and the 2013 publication of the Next Generation Science Standards, which explicitly connect science concepts and practices to those of engineering, have elevated the idea of integration as a potential component of STEM education. Recognizing that education within the individual STEM disciplines has great value and that efforts to improve discipline-centered teaching and learning should continue, this project considers the potential benefits—and challenges—of an explicit focus on integration. The report’s primary audience is education researchers and those working in the cognitive and learning sciences. It is these individuals to whom the committee’s research agenda is directed. However, the report contains much more than the agenda. It should also prove useful to the large, diverse set of individuals directly involved in or supportive of efforts to improve STEM education in the United States. These include educators, school leaders, curriculum and assessment developers, and those engaged in teacher education and professional development, as well as policymakers and employers.