School administrators are expected to undertake a variety of roles and responsibilities with regard to facilitating the ongoing professional development of teachers in their schools. Administering formal or informal mentoring initiatives is a typical strategy employed for supporting early career teachers [ECTs] as they adjust to school culture, contexts, and individual responsibilities. Implementation of mentoring programs happens within a dynamic contextual landscape that both influences the development of educational and professional expectations for instruction and professional learning and shapes the school’s culture. In this article, drawing on the international multi-factor systematic review of research literature, we sought to establish how contextual factors, such as culture, political systems, social practices, and organizational structures, influence early career teaching and describe the implications of these contextual factors for school leaders’ involvement in and administration of mentoring programs. After a brief description of theoretical framing and our systematic review method and sampling procedures, we synthesize the findings from the extant literature on each of the contextual factors and discuss their influence on school leaders’ involvement in mentoring. Finally, we discuss the complexity of contexts and practices in mentoring ECTs and conclude with the implications for policy, practice, and future research.