This paper explores the causes behind the severe underrepresentation of women in engineering. Based on national data on undergraduate engineering programs, this study presents cross-sectional estimates of male and female student retention. Contrary to widespread beliefs, the study found that overall and in most disciplines there is no differential attrition by gender. Instead, results suggest that gender disparities in engineering are largely driven by inadequate enrollment (not inadequate retention) of women. The paper concludes that outreach within institutions of higher education, across institutions (into two-year colleges, middle and high schools), and into K-12 curricular reformare needed to address what is, at its very core, a recruitment problem.