Among the many challenges facing public schools are high levels of principal turnover. Given the important role that principals play and are expected to play in the improvement process, concerns about principal turnover have resulted in a growing body of research on its causes and consequences. The purpose of this review is to take stock of what we have learned about the sources and consequences of principal turnover and to identify what gaps remain. The final review included 36 empirical studies. It discusses and categorizes findings relating to the determinants and consequences of principal turnover. The review concludes with a discussion about the implications of those findings and the areas and kinds of research still needed.