This Brief synthesizes findings from recent experiments on jealousy in infants with insights from pioneering thinkers in developmental science. It discusses attachment issues, status of jealousy as an emotion and as a feature of temperament, underpinnings in social cognition, the development of adaptive versus maladaptive presentations, and facets of  jealousy that may be part of a normal repertoire of coping strategies. This unique volume also identifies facial, vocal, and bodily responses associated with jealousy as well as situations of differential treatment by caregivers that may bring them about. This knowledge is as useful in studying children's emotional development as it is in addressing jealousy-based challenges in growing families. Among the featured topics:  Jealousy in infants, defended and defined. A theory of jealousy as temperament. Sadness, anger, fear, and love. Individual differences and normativity. Child and contextual influences on individual differences. Implications for clinical intervention: preparing for a sibling's arrival. Jealousy in Infants is an essential resource for researchers, clinicians, and graduate students in developmental psychology, infant mental health, and social psychology.