This thesis addresses two questions. One concerns the metaphysics of emotions and asks what kinds of mental states emotions are. The other asks how the metaphysics of emotions bears on first and third-personal knowledge of emotions. There are two prevailing views on the nature of emotions. They are the perception and cognitive views. The perception view argues that emotions are bodily feelings. The cognitive view, by contrast, contends that emotions are some sorts of evaluative judgments. I show that both views provide inadequate accounts of the nature of emotions. The perception view fails to do justice to the fact that emotions may not involve any bodily feeling. The cognitive view, by contrast, cannot account for the fact that emotions are states that adult humans have in common with infants and animals. On the basis of these criticisms, I put forward an alternative account of emotions. This involves five main arguments. The first is that emotions are enduring non-episodic dispositions that may or may not manifest themselves in experiential episodes such as emotional feelings and behaviour episodes such as expressions. The second argument is that emotional feelings are perceptions of specific bodily changes brought about by emotions. These feelings serve as clues as to what kinds of emotions the subject has. The third argument is that expressions are observable manifestations of emotions in virtue of which emotions can be perceived and subsequently known, directly and non-inferentially, by other people. The fourth argument is that when someone has an emotion without feeling it, she can still come to know it by believing true ascriptions that other people make about the emotion they perceive in her expression. The fifth argument is that full knowledge of emotions requires knowledge of the emotion objects.