Women continue to be underrepresented in science, technology, engineering, and mathematics (STEM). This literature review examines psychological factors over the course of development that contribute to the ongoing underrepresentation of women in these fields. The authors present fundamental principles that pose barriers to women in STEM."Math class is tough!" complained Teen Talk Barbie dolls in 1992. The nownotorious statement spurred controversy in the science, technology, engineering, and mathematics (STEM) community, resulting in Mattel's offering to trade an inoffensive version of the doll for the ones that were programmed to say the phrase ("Mattel Says," 1992). In a letter addressing the controversy, Mattel's president indicated that, although the company considered the statement to be a sentiment shared by many male and female students, "We didn't fully consider the negative implications of this phrase."Perhaps the doll would not have been the target of criticism if it were not released in a society in which boys continually outscore girls in STEM-related advanced placement exams (American Association of University Women [AAUW], 2010), teachers evaluate their male students' mathematical ability as being higher than that of female students despite performance measures that indicate roughly equal ability (Tiedemann, 2000), and women are considered less likable for demonstrating competence in a predominantly male discipline (Heilman, Wallen, Fuchs, & Tamkins, 2004). Hearing "Math class is tough!" from a child's doll is particularly troubling for numerous parents, educators, and researchers because they understand how its message operates within a social context that repeatedly discourages women and girls from entering and succeeding in STEM fields.