In recent years there has been a growth in support, guidance and orientation programs – collectively known as induction – for beginning elementary and secondary teachers during the transition into their first teaching jobs. While the particulars of such programs vary widely, they are generally intended to increase the confidence and effectiveness of new teachers, and thus to stem the high levels of attrition among beginning teachers, which estimates place as high as 40-50% within the first five years. Over the past two decades, numerous studies have been done on a variety of different types of induction programs, and this research has been widely cited by both advocates and reformers. It is unclear, however, whether the soundness of much of this research truly justifies the conclusions often taken from it. To help address this issue, the Education Commission of the States commissioned the present effort as a comprehensive and critical review of existing empirical studies on induction programs. This report's primary objective is to provide policymakers, educators and researchers with a reliable assessment of what is known, and not known, about the effectiveness – the value added – of teacher induction programs. In particular, this review focuses on the impact of induction and mentoring programs on teacher retention.