Stereotypes reduce women's identification with science, technology, engineering, and math (STEM), which can decrease their motivation to enter STEM domains. Stereotypes may be gender-based (e.g., STEM is for men) or trait-based (e.g., STEM is for geniuses). In this study, I explored two primary research questions: First, would stereotyping STEM as a domain for nerdy geniuses negatively relate to women's STEM identity? Second, would STEM identity mediate the relation between stereotypes and STEM motivation? Nerd-genius stereotypes and gender stereotypes negatively contributed to women's STEM identity. STEM identity positively contributed to women's STEM motivation (including expectancy-value beliefs). Participants were a diverse sample of undergraduate women (N ¼ 195, mean age was 19.8; 30% of participants were Latina, 30% European, 24% Asian). Stereotype measures were (1) implicit gender-STEM associations, (2) explicit gender associations about STEM, and (3) a new scale that measured nerd-genius stereotypes. The results highlight the unique contribution different stereotypes make toward women's identification with STEM and, in turn, their motivation to pursue STEM pathways. Practice implications include addressing nerd-genius stereotypes in STEM interventions and reducing classroom artifacts that might be reminiscent of these stereotypes.