In an era when women are increasingly prominent in medicine, law, and business, why are there so few women scientists and engineers? A 2010 research report by AAUW presents compelling evidence that can help to explain this puzzle. <em>Why So Few? Women in Science, Technology, Engineering, and Mathematics</em> (STEM) presents in-depth yet accessible profiles of eight key research findings that point to environmental and social barriers — including stereotypes, gender bias, and the climate of science and engineering departments in colleges and universities — that continue to block women’s progress in STEM. The report also includes up-to-date statistics on girls’ and women’s achievement and participation in these areas and offers new ideas for what each of us can do to more fully open scientific and engineering fields to girls and women.