This study uses longitudinal data of undergraduate students from five public land-grant universities to better understand undergraduate students' persistence in and switching of majors, with particular attention given to women's participation in science, technology, engineering, and mathematics (STEM) fields. Specifically, the study examines patterns of behavior of women and minorities in relation to initial choice of college major and major field persistence, as well as what majors students switched to upon changing majors. Factors that impact major field persistence are also examined, as well as how switching majors affects students' time-to-degree. Using a broad definition of STEM, data from nearly 17,000 undergraduate students were analyzed with descriptive statistics, cross tabulations, and binary logistic regressions. The results highlight women's high levels of participation and success in the sciences, challenging common notions of underrepresentation in the STEM fields. The study calls for researchers to use a comprehensive definition of STEM and broad measurements of persistence when investigating students' participation in the STEM fields.