STEM careers are among the fastest growing and highest paid occupations throughout the world. However, persistent social inequities in STEM domains emerge early for Black and Latinx adolescents, creating numerous barriers to their pursuit of STEM. Developmental and motivational theories highlight parents as a source of strength and support for students’ STEM motivational beliefs. We conducted a systematic review of the existing work on parents’ STEM socialization processes that shape Black and Latinx adolescents’ STEM motivational beliefs. As part of this goal, we examined the variability within Black adolescents and within Latinx adolescents based on (a) other demographic factors (e.g., gender) and (b) racial/ethnic promotive and inhibitive factors (e.g., racism). The systematic literature search and eligibility screening yielded 36 relevant peer-reviewed, empirical journal articles published between January 2000 and January 2020. Overall, a majority of studies found support for positive relations between parents’ STEM-specific support and adolescents’ motivational beliefs among Black and Latinx families. Additionally, most studies included analyses within each racial/ethnic group, and about half of all articles included racial/ethnic promotive or inhibitive factors, such as familism or racism. In our discussion, we highlight an agenda for future research and discuss bridging theoretical perspectives to better position research to more accurately describe STEM motivation among youth from historically underrepresented groups.