Teachers are the engine that drives social and emotional learning (SEL) programs and practices in schools and classrooms, and their own social-emotional competence and wellbeing strongly influence their students. But when teachers poorly manage the social and emotional demands of teaching, students' academic achievement and behavior both suffer. How can we boost teachers' social-emotional competence, and how can we help them create the kind of classroom environment that promotes students' SEL? In this article, Kimberly Schonert-Reichl reviews the results of several interventions that have specifically sought to improve teachers' social-emotional competence and stress management in school, many of which are promising. She also shows how teachers' beliefs--about their own teaching efficacy, or about whether they receive adequate support, for example--influence the fidelity with which they implement SEL programs in the classroom. When fidelity is low, SEL programs are less successful. Finally, she examines the extent to which US teacher education programs prepare teacher candidates to promote their own and their students' social-emotional competence.