"This article develops a supply-side mechanism about how cultural beliefs about gender differentially influence the early career-relevant decisions of men and women. Cultural beliefs about gender are argued to bias individuals' perceptions of their competence at var- ious career-relevant tasks, controlling for actual ability. To the extent that individuals then act on gender-differentiated perceptions when making career decisions, cultural beliefs about gender channel men and women in substantially different career directions. The hy- potheses are evaluated by considering how gendered beliefs about mathematics impact individuals' assessments of their own mathe- matical competence, which, in turn, leads to gender differences in decisions to persist on a path toward a career in science, math, or engineering."