Informed by recent developments in economics and psychology, this project defends and develops a substantive philosophical account of the nature of happiness. It is argued that happiness is best seen as a positive emotional response. Crucial to such an understanding is that, like other emotions, happiness picks out a psychological state with inherent and usually non-psychological conditions of appropriateness. Like fear is an appropriate response to danger, and anger to injustice, happiness is an appropriate response to good things happening. Happiness is normatively significant only when its conditions of appropriateness are being met. This account avoids a dilemma that is generated by hedonism, which implausiby restricts leading a happy life to feeling happy, and eudaimonistic objective-list accounts, which implausibly allow that one could become happier despite feeling less happy. The project explores the ramifications of this account of happiness to various philosophical, psychological, economic, and political issues.