The positive emotion of happiness reflects a moderate level of arousal. Their empirical analyses of children’s understanding of emotion labels during early childhood also show a gradual differentiation from a basic distinction between positive and negative emotion to a more nuanced understanding of the different negative emotions. A body of work testing differential emotions theory has focused on patterns of emotional expression that could be discerned across ages and cultures. Emotion is regulated both through internal physiological and cognitive processes and through learning about the social rules that control displays of emotion in particular families and cultures. In humans, emotion is expressed through different channels: the face, the voice, the hands and the physiological reactions of the body. As children grow older, their emotions are regulated by social learning and their growing understanding of the world. The chapter also presents an overview of the key concepts discussed in this book.