Awareness of underrepresentation in science, technology, engineering, and mathematics (STEM) fields in the United States has grown, including the release of several national reports highlighting the issues both for those excluded and the STEM enterprise. At the same time, research on underrepresented groups in STEM education has grown substantially. Advances in theory and methods have allowed for concomitant expansion in research-based strategies that could change the calculation for people of color, women and girls, people with disabilities, first-generation college students, and other groups in STEM education. This session's focus is broad, including research involving various groups and education levels, from elementary through the professoriate. Additionally, research findings include individual- and group-level studies that investigate behavioral, cognitive, learning, and social differences as well as organization, institution, or system processes that may affect participatory variations in STEM learning. The intent is to showcase the breadth and rigor of this work and foster discussion about how this research may inform practice and future directions. While the focus is on the United States, the lessons learned have potential to inform efforts in other countries to understand the causes and consequences of underrepresentation. U.S. researchers will benefit from the international forum and discussions about alternative approaches across national borders and cultures.