Only when teachers have had the kind of training and experience that makes them successful with students can schools become and remain effective. Creating the conditions to retain strong teachers preserves this essential human capital; hiring, training, and losing new teachers is a costly vicious cycle. Evidence suggests that attrition is a much greater problem in the teacher supply picture than is producing enough teachers to fill the nation’s needs. School leaders need to understand the reasons for teacher attrition if they are to develop effective strategies for building and maintaining a strong science teaching force. In this chapter, the authors discuss what influences science teacher recruitment and retention and what science leaders in teaching, teacher education, professional development, and school administration can do to address this problem.