The U.S. federal government identifies many science, technology, engineering, and math (STEM) majors as "areas of national need" that are "crucial to national innovation, competitiveness, and well-being and in which not enough students complete degrees." Underrepresentation of women in STEM in the United States has economic consequences, both individually and nationally. For example, given the ongoing connection between individuals' technological skills and their economic opportunities, women's economic independence may be hindered by underparticipating in the technological industries of the twenty-first century. Further, in light of the national call to action for research in science and technology, women's underrepresentation in STEM signifies a loss of potential talent and innovation that may have an impact on the ability of the United States to remain globally competitive in science and engineering. The technological and scientific professional workforce stands to benefit from diverse perspectives. Creating opportunities for more women to enter and be successful in STEM fields will contribute to diversifying STEM perspectives, ultimately making scientific research more vigorous and complete. Given that women's underrepresentation in the STEM workforce is largely rooted in their selection of college major, this article summarizes the factors that contribute to women's selection of and persistence in STEM majors. The authors begin with a review of how the educational context shapes women's interest in STEM, and then they move to an overview of the major social and cultural influences beyond the classroom. The article concludes with a discussion of the utility of this information for institutional researchers and how they might further study issues of gender and STEM on their own campuses.