In one important sense, 'happiness' refers to an emotion. This emotion–sometimes labelled 'joy'–is central in our mental lives, and yet it has been neglected by philosophers. This book investigates the emotion of happiness, and especially the question of when it is appropriate, or fitting. If someone is happy about a certain politician's death, you might think that their happiness is inappropriate; whereas happiness about your recent promotion seems perfectly appropriate. Cases like these suggest a more general idea: that happiness can be more or less appropriate, depending on what it is directed at. A compelling view is that happiness is fittingly directed at good things, and sadness at bad things, but this basic idea leaves many questions open: What is happiness? Why is it important? When is it fitting? Why should we care whether our happiness is fitting? Why think that happiness is an especially important emotion? Can hedonic adaptation possibly be rational? To answer these questions, Alex Gregory explores the nature of happiness, the nature of fittingness, and their interaction, and in this way breaks fertile new ground in the philosophy of emotion and value.