For public managers facing political and structural constraints, transformational leadership promises to meaningfully improve outcomes by communicating an inspiring vision of the organization. But this promise rests to a great degree upon the communication skills and behaviors of the leader. A better understanding of how transformational leadership functions in organizations therefore requires a deeper application of theory from the field of communication. We explore the question of what communication behaviors facilitate transformational leadership. We apply a media richness framework to propose that transformational leaders will be most effective when employing a face-to-face dialogue approach to communication. Using a multi-source longitudinal research design, we find support for this proposition in an empirical test on 256 Danish tax units, lower- and upper secondary schools, childcare centers, and bank branches. We also find that size matters, with the effectiveness of face-to-face dialogue declining as the organization becomes larger.