In this conceptual article, we present a theoretical framework designed to illustrate the many contexts and factors that interact and shape the work of mentor teachers. Drawing on the literature on K-12 teaching and on teacher preparation, we argue for greater acknowledgment of the complex work of mentor teachers as they navigate multiple contexts. We conclude by considering how this framework helps us to better understand the work of mentor teachers and by offering suggestions for teacher preparation programs and K-12 schools to better support mentor teachers and best prepare teacher candidates.