Women continue to be underrepresented in mathematically intensive majors like economics in the US. This column examines whether women’s colleges, and in particular Wellesley College, affect choice of major. Women who are accepted to Wellesley and choose to enroll there are about 81% more likely to major in economics than those who choose to enroll elsewhere. The authors attribute some of this ‘Wellesley effect’ to the fact that women make up more of the faculty in economics at Wellesley than at other institutions that Wellesley-admitted students attend. These results strongly suggest that the environment affects major choice.