Findings from several studies suggest that teachers who embrace an autonomy-supportive style vis-à-vis their students promote student motivation. However, the question of what makes teachers adopt this supportive style remains unanswered. Using Self-Determination Theory as a framework, we suggest that teachers' own motivation and their beliefs about student motivation are predictors of their tendency to opt for an autonomy-supportive rather than a controlling style. One hundred and fifty-four teachers completed a questionnaire designed to assess their type of motivation to teach, what they believe is desirable student motivation, and the level to which they opt for behaviors that support student autonomy. Our findings suggest: Firstly, that teachers who teach out of interest and enjoyment, and value their work (autonomous motivation), tend to believe that the learning of students who are autonomously motivated benefits more; secondly, that teachers who believe that autonomous motivation is desirable for their students' learning also tend to opt for an autonomy-supportive rather than a controlling style; thirdly, that teachers who are autonomously motivated themselves are more likely to adopt an autonomy-supportive style, especially when they also believe that autonomous motivation is desirable for their students' learning. The study's findings highlight the importance of a teacher's own motivation and beliefs as factors that promote autonomy-supportive behavior in the classroom.