To improve our understanding of the factors that influence persistence rates in STEM field majors, the Alfred P. Sloan Foundation provided a grant to the Cornell Higher Education Research Institute in 2007 to study the question. The five papers in the symposium represent the output of the project. This introduction explains the motivation for undertaking the study, describes the questions the researchers asked and the data bases they used in their studies, summarizes their findings, and suggests directions for future research.