In this study, the authors examined the relationship between teacher and student enjoyment. Based on social-cognitive approaches to emotions, they hypothesized (a) that teacher enjoyment and student enjoyment within classrooms are positively linked and (b) that teacher enthusiasm mediates the relationship between teacher and student enjoyment. Self-reported enjoyment of mathematics classes was available from 1,542 students from 71 classrooms at 2 time points (Grades 7 and 8). At Time 2, mathematics teachers' reports of their enjoyment of teaching were available (N = 71), as well as student ratings of teacher enthusiasm. The findings were in line with theoretical expectations. Multilevel structural equation modeling showed that teacher and student enjoyment were positively related even when the authors adjusted for students' previous-class levels of mathematics enjoyment, and that the effect of teacher enjoyment on student enjoyment was mediated by teacher enthusiasm. Discussion centers on the practical implications for affective interactions in the classroom. (Contains 1 figure, 2 tables, and 3 footnotes.)