In this article, we briefly review conceptual, theoretical, and empirical knowledge about a rapidly developing topic of organizational research, workplace mistreatment (e.g., bullying, mobbing, abuse, aggression) as well as our research about principal mistreatment of teachers. Following this, we discuss the importance of preparing prospective and practicing school principals to deal with personal and organizational factors that may interact to produce the kinds of leadership that seriously damage teachers, teaching, and student learning.