Developmental psychologist Jerome Kagan, speaking with Yale's June Gruber for the Experts in Emotion series, discusses his decades of research on temperament. Kagan traces what drew him to the study of emotion and walks through the central findings from his work at Harvard, including his research on how infants' physiological reactivity predicts later differences in shyness and boldness. He addresses where he sees the field heading next and closes with practical advice for students considering research careers in emotion science. The format is a seated interview, structured around chapter markers moving from his early interests through his major discoveries to his outlook on the field's future. It is a compact but substantive conversation with one of the most influential figures in temperament research, useful as an introduction to how longitudinal studies of infant reactivity shaped modern developmental psychology.