"Increasing attention is being paid to the importance of trust in organizations generally, and schools in particular, as an essential ingredient of improvement and effectiveness. The role of trust in leadership and in leaders’ interactions with subordinates has been especially emphasized. In a study of the emotions of teaching that included data concerning teachers’ recollections of emotionally positive and negative interactions with their colleagues, teachers made almost no explicit references to trust as a source of positive emotion among their colleagues. In other words, in their lateral relations with colleagues, trust was absent or taken for granted. However, what teachers did report as one of the strongest sources of negative emotion with their colleagues was evidence of the opposite of trust - betrayal. The present paper draws on this interview-based study with 50 Canadian teachers in 15 elementary and secondary schools to examine the nature and effects of betrayal among colleagues in teaching. It documents three forms of betrayal: competence, contract, and communication betrayal. Betrayal in teaching is signifcant not only in a moral sense, but also because its consequence is to lead to teachers to avoid conflict and interaction with each other, and thereby insulate themselves from the opportunities for learning and constructive disagreement. The paper concludes by arguing that if schools are going to become stronger professional learning communities, they must seek not only to establish trust in teaching, but also to avoid the causes of pervasive betrayal."