What is an emotion? Can emotion be measured? How can we know if a person is experiencing an emotion? In this sophisticated overview of human emotions, a widely respected psychologist and author addresses the ambiguities and embraces the controversies that surround this intriguing subject. An insightful and lucid thinker, Jerome Kagan examines what exactly we do know about emotions, which popular assumptions about emotions are incorrect, and how scientific study must proceed if we are to uncover the answers to persistent and evasive questions about emotions. Integrating the findings of anthropological, psychological, and biological studies in his wide-ranging discussion, Kagan explores the evidence for great variation in the frequency and intensity of emotion among different cultures. He also discusses variations among individuals within the same culture and the influences of gender, class, ethnicity, and temperament on a person’s emotional patina. In his closing chapter, the author proposes that three sources of evidence—verbal descriptions of feelings, behaviors, and measures of brain states—provide legitimate but different definitions of emotion. Translating data from one of these sources to another may not be possible, Kagan warns, and those who study emotions must accept—at least for now—that their understanding is limited to and by the domain of their information.