In this article, some of the ways in which thinking about chaos theory can help teachers and student-teachers to accept uncertainty and randomness as natural conditions in the classroom are considered. Building on some key features of complex systems commonly attributed to chaos theory (e.g. complexity, nonlinearity, sensitivity to initial conditions), and using examples from student teachers' descriptions of problematic classroom situations, the author finds these features of complex systems highly relevant for language teaching. The author suggests that teacher educators should help students to accept the complexity and unpredictability of teaching as natural conditions and become 'agents of chaos' in the classroom. In order to accomplish this task, teacher educators should accept the complexity and unpredictability of their own teaching environments, thus creating new possibilities for their students' learning and development as teachers.