The negative impacts of high teacher turnover are widely documented, with particular impact on low-income, high-minority schools. Turnover can be especially widespread in science education, where teachers are in high demand. Although teacher retention is predicated on job satisfaction, which is in turn fostered by opportunities for professional growth, little research has been conducted on the relationship between professional development and retention. In order to investigate this relationship, we conducted a mixed methods study to first quantitatively determine the relationship between professional development and retention, and then qualitatively investigate the nature of the relationship. The results demonstrate a complex relationship, in which professional identity, professional development, and agency contribute iteratively to teachers remaining in middle school science teaching.