There is a need to help more students succeed in science, technology, engineering, and mathematics (STEM) education, with a particular interest in reducing current gender gaps in STEM motivation and participation. This integrative review synthesizes a body of work suggesting that social factors, such as stereotypes and self-representations about “belonging,” provide explanatory mechanisms for the observed gender differences in STEM interest and academic outcomes. First, we examine how cultural stereotypes specific to STEM contribute to gender gaps by negatively impacting interest and academic outcomes. Second, we review the central role of the self-representations affected by those stereotypes, including the particular importance of a sense of belonging in STEM. Third, we discuss various interventions that buffer against stereotypes and enhance a sense of belonging to improve interest and academic outcomes. We find that STEM gender gaps in interest and academic outcomes are malleable and can be changed through interventions. Finally, we suggest directions for future research. By organizing the research in this way, our review and theoretical analysis clarifies key factors contributing to the current gender gaps in STEM and mechanisms by which psychological interventions can help address and reduce STEM gender gaps.