Emotions play an important role in the work of teachers serving students with emotional and behavioral disabilities (EBD), yet little is known about teachers' momentary affective experiences. In this study, we collected 710 surveys regarding momentary affect from 14 teachers of students with EBD. We used descriptive analysis and variance decomposition to examine the frequency, intensity, and variability of these experiences. We then tested a series of models to explore how specific professional activities relate to teachers' momentary affect. We found that teachers experienced positive affect more frequently and intensely than negative affect and that large proportions of the variation in positive and negative affect can be attributed to variation within individual teachers across time points. For these teachers, engaging in discipline was significantly associated with a higher negative affect, whereas engaging in instructional activities was associated with a higher positive affect. We discuss implications for researchers and practitioners. [For the corresponding grantee submission, see ED627065.]