Research on second and foreign language learning suggests that the expectations that teachers form for their students can often have an impact on students' behavior and achievement. Some teachers tend to convey differential expectations to students, which appear to have self-fulfilling prophecy effects on them. The self-fulfilling prophecy effects of teacher expectations are an important, yet not adequately appreciated affective variable in second and foreign language learning. In this article we present the theoretical background on teacher's expectations for their students. We also describe the sources of teachers' expectations and the ways through which teachers communicate expectations to students. We finally deal with the pedagogical implications, offering suggestions about how teachers might become more successful in communicating high expectations.