The need for school principals to implement teacher-supportive leadership practices is paramount to students' learning. The present study synthesized the disparate fields of educational leadership and educational psychology in an effort to investigate the effects of principal leadership styles on teacher motivation. Specifically, the effects of the principal leadership styles of authoritarian, democratic, or laissez-faire practices on teachers' motivation were investigated from the theoretical framework of Self-Determination Theory (SDT). Results from a survey indicated that principals' leadership styles were significantly related to the combined dependent variables of teacher autonomy, relatedness, competence, and social isolation. Specifically, the results of post hoc tests indicated that teachers reported higher levels of autonomy, relatedness, and competence under a principal who was perceived to demonstrate a democratic leadership style. Moreover, administrators who were