Abstract: This literature review examines the nature of the existing academic gender gap in the United States' (U.S.) mathematics, science, and engineering (SME) fields. First, a review of the most recent academic data at the secondary level, along with ACT, PISA, and TIMSS scores, reveal no gender differences in performance or participation between men and women. The SAT is an exception, as it still reflects gender differences. At post secondary through graduate levels, no performance differences exist between men and women in any of the SME fields. At the bachelors and masters levels, women have caught up in mathematics, moving toward equity in physical sciences; however, their participation in engineering is considerably less than it is for men. In contrast, at doctoral levels, women participate considerably less than do men in all SME fields. The academic data also shows an alarming trend. Overall, fewer males and females are participating in the SME fields, especially engineering, with foreign students having to compensate for this slack. A literature review of stereotype threat (Steele & Aronson, 1995), its moderating factors, its effects on women in SME fields, and its mediating effects are also presented. Stereotype threat (ST) is a situational predicament causing members of any group to underperform during a challenging test when a negative stereotype about their in-group is made salient (Steele & Aronson, 1995). The underlying causes of stereotype threat are reviewed. Growing evidence seems to identify that both affective and cognitive mechanisms underlay ST, with heightened arousal representing the former and decreased working memory capacity (Schmader & Johns, 2003), increased disruptive mental load (Croizet et al., 2004), and increased negative thinking representing the latter. Research has ruled out anxiety as a possible mediator of ST. Short summaries on 'nature' (biological) and 'nurture' (environmental) based studies pertaining to the SME gender differences are also presented. A comparison of nature, nurture, and ST models show that women's lack of participation and lower mathematics scores on some standardized tests are neither due to innate, nor to internalized, psychological factors. Rather, they reflect a situational effect due to ST. ST research shows that 3-D mental rotation gender differences, which constitute the basis of the nature arguments, are due to situational and external factors, and simple interventions can remove these gender differences during laboratory settings. Experiments measuring any abilities subject to stereotyping need to address ST as a possible confounding factor. Available academic data along with ST studies, therefore, provide strong counter arguments to both dominant nature and nurture views. Suggestions for future research and possible interventions are included.