Although girls and boys appear equally interested in most STEM fields during childhood and adolescence, men pursue academic research careers in most of these same fields at higher rates than women. We tested several prominent hypotheses concerning the causes of this differentiation. Specifically, 136 (59 women) doctoral students in the United States completed measures of their occupational values, views of the degree to which STEM careers afford their values, perceptions of gender discrimination in their department, mentor support, and satisfaction with their graduate training. Results indicated gender differences in students’ occupational values, ratings of career value affordances, and perceptions of gender discrimination. The perception that a STEM research career affords one’s values was predictive of women’s (but not men’s) satisfaction with their graduate training.