Students in introductory STEM courses often have concerns about whether they will be academically successful in large university courses/but many have an additional concern that maybe “people like me don’t belong in this course.” This concern is called belonging uncertainty and is related to the insecurity someone feels because of their identities. In our group/we are studying the effect that course-level student belonging has on student performance and retention in that course. We have found at two different institutions/course-level belonging affects student performance in large general chemistry and introductory physics courses. Expanding upon these studies/we are interested in understanding the mechanism of how social belonging affects course performance and retention. One step in determining the mechanism is to explore the characteristics of the course that students use when describing their sense of belonging and belonging uncertainty. Our goal is to help instructors create course environments that support and encourage all students to reach their potential and continue to pursue careers in STEM or healthcare.