Emotions are a central part of our existence. The nature, causes, and corollaries of emotions have been investigated in various scientific disciplines, from philosophy and sociology to psychology and biology. In this chapter we aim to contribute to our current understanding of emotions. We take a psychological perspective on emotions, with a particular focus on their roles in educational settings. We discuss both students' and teachers' emotions. First, we define emotions and outline different ways of measuring them. We then present findings demonstrating their causes and their effects on individuals' cognition, learning, and achievement. Finally, we outline avenues for designing emotionally healthy learning environments.